Solid electrolyte composition, solid electrolyte-containing sheet, electrode sheet for all-solid state secondary battery, all-solid state secondary battery, method of manufacturing solid electrolyte-containing sheet, and method of manufacturing all-solid state secondary battery

ABSTRACT

A solid electrolyte composition includes: an inorganic solid electrolyte (A) having ion conductivity of a metal belonging to Group 1 or Group 2 in the periodic table; a binder (B); and a dispersion medium (C), in which the binder (B) includes a first binder (B1) that precipitates by a centrifugal separation process and a second binder (B2) that does not precipitate by the centrifugal separation process, the centrifugal separation process being performed in the dispersion medium (C) under a specific condition, and a content X of the first binder (B1) and a content Y of the second binder (B2) satisfy the following expression,0.10≤Y/(X+Y)≤0.80.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of PCT International Application No.PCT/JP2018/37734, filed on Oct. 10, 2018, which claims priority under 35U.S.C. § 119(a) to Japanese Patent Application No. 2017-221842, filed onNov. 17, 2017. Each of the above application(s) is hereby expresslyincorporated by reference, in its entirety, into the presentapplication.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a solid electrolyte composition, asolid electrolyte-containing sheet, an electrode sheet for an all-solidstate secondary battery, an all-solid state secondary battery, a methodof manufacturing a solid electrolyte-containing sheet, and a method ofmanufacturing an all-solid state secondary battery.

2. Description of the Related Art

A lithium ion secondary battery is a storage battery which has anegative electrode, a positive electrode, and an electrolyte sandwichedbetween the negative electrode and the positive electrode and enablescharging and discharging by the reciprocal migration of lithium ionsbetween both electrodes. In the related art, in lithium ion secondarybatteries, an organic electrolytic solution has been used as theelectrolyte. However, in organic electrolytic solutions, liquid leakageis likely to occur, there is a concern that a short circuit and ignitionmay be caused in batteries due to overcharging or overdischarging, andthere is a demand for additional improvement in safety and reliability.

Under these circumstances, all-solid state secondary batteries in whichan inorganic solid electrolyte is used instead of the organicelectrolytic solution are attracting attention. In all-solid statesecondary batteries, all of the negative electrode, the electrolyte, andthe positive electrode are solid, safety and reliability which areconsidered as problems of batteries in which the organic electrolyticsolution is used can be significantly improved, and it also becomespossible to extend the service lives. Further, an all-solid statesecondary battery may have a laminate structure in which electrodes andan electrolyte are directly disposed in series. Therefore, the energydensity can be further increased as compared to a secondary battery inwhich an organic electrolytic solution is used, and the application toan electric vehicle or a large-sized storage battery is expected.

In order to put the all-solid state secondary battery into practice, aninvestigation on a material for forming a solid electrolyte layer, apositive electrode or negative electrode active material layer, or thelike has actively progressed.

In order to increase the energy density of the all-solid state secondarybattery, it is necessary to laminate the solid electrolyte layer and theelectrode active material layers. This lamination is typically performedunder a pressurization condition. Therefore, in a case whereadhesiveness between solid particles forming a layer is not sufficient,a defect such as cracking is likely to occur.

In order to improve binding properties between solid particles formingthe solid electrolyte layer and the electrode active material layer, itis considered to add a binder formed of a resin to a material forforming each of the layers. However, in general, the binder does nothave ion conductivity. Accordingly, in a case where the binder is added,the resistance increases, and it is difficult to obtain a secondarybattery having a desired conductivity.

As a technique of dealing with this problem, for example, JP2015-088486Adescribes a solid electrolyte composition including: an inorganic solidelectrolyte; binder particles having a specific particle size that isformed of a polymer including a macromonomer as a component; and adispersion medium. According to the technique described inJP2015-088486A, by using the solid electrolyte composition for formingeach of the above-described layers, an increase in interface resistancecan be suppressed while improving binding properties between the solidparticles.

SUMMARY OF THE INVENTION

It is assumed that a solid electrolyte layer and electrode activematerial layers (a positive electrode active material layer and anegative electrode active material layer) forming an all-solid statesecondary battery are prepared in a sheet shape while being wound usinga roll-to-roll method for mass production. In addition, regarding theshape of the all-solid state secondary battery itself, it is assumedthat a battery sheet having a configuration in which the solidelectrolyte layer and the electrode active material layers are laminatedto enter a roll-shaped (cylindrical) laminate state such that the outputof the battery increases. Accordingly, for the solid electrolyte layerand the electrode active material layers, a characteristic ofsuppressing the occurrence of a defect even during bending is requiredin addition to suppression of a defect under the above-describedpressurization condition.

Therefore, an object of the present invention is to provide a solidelectrolyte composition that can suppress the occurrence of a defect(chipping, cracking, fracturing or peeling) in a layer even afterbending with a smaller bend radius and can allow a layer havingexcellent ion conductivity to be formed even after the bending.

In addition, another object of the present invention is to provide asolid electrolyte-containing sheet in which the occurrence of a defectin the layer even after bending with a smaller bend radius is suppressedand excellent ion conductivity can be exhibited even after the bending,an electrode sheet for an all-solid state secondary battery, anall-solid state secondary battery, a method of manufacturing anelectrode sheet for an all-solid state secondary battery, and a methodof manufacturing an all-solid state secondary battery.

The present inventors repeatedly conducted a thorough investigation inconsideration of the above-described objects. As a result, it was foundthat, in a solid electrolyte composition used for forming a solidelectrolyte layer and an electrode active material layer forming anall-solid state secondary battery, by using not only a specific amountof a particle polymer that is insoluble in a dispersion medium of thecomposition but also a specific amount of a polymer that is stablydispersed in a supernatant without precipitating even after anultracentrifugal separation process under a specific condition in thedispersion medium of the composition (a polymer that is soluble in thedispersion medium of the composition or is present in the form of fineparticles having a small particle size in the dispersion medium) incombination instead of simply using the particle polymer, theabove-described objects can be achieved. The present invention has beencompleted based on the above findings as a result of repeatedinvestigation.

That is, the above-described objects have been achieved by the followingmeans.

[1] A solid electrolyte composition comprising:

an inorganic solid electrolyte (A) having ion conductivity of a metalbelonging to Group 1 or Group 2 in the periodic table;

a binder (B); and

a dispersion medium (C),

in which the binder (B) includes a first binder (B1) that precipitatesby a centrifugal separation process and a second binder (B2) that doesnot precipitate by the centrifugal separation process, the centrifugalseparation process being performed in the dispersion medium (C) at atemperature of 25° C. at a centrifugal force of 610000 G for 1 hour, and

a content X of the first binder (B1) and a content Y of the secondbinder (B2) satisfy the following expression by mass,0.10≤Y/(X+Y)≤0.80.

[2] The solid electrolyte composition according to [1],

in which a glass transition temperature of a polymer forming the secondbinder (B2) is −50° C. to 10° C.

[3] The solid electrolyte composition according to [1] or [2],

in which the dispersion medium (C) includes a hydrocarbon solvent.

[4] The solid electrolyte composition according to any one of [1] to[3],

in which a particle size of the first binder (B1) is 10 to 10000 nm.

[5] The solid electrolyte composition according to any one of [1] to[4],

in which in a case where the solid electrolyte composition does notinclude an active material (D), the content Y of the second binder (B2)and a content Z of the inorganic solid electrolyte (A) satisfy thefollowing expression by mass, and

in a case where the solid electrolyte composition further includes theactive material (D), the content Y of the second binder (B2) and a sum Zof the content of the inorganic solid electrolyte (A) and a content ofthe active material (D) satisfy the following expression by mass,0.001≤Y/(Y+Z)≤0.1.

[6] The solid electrolyte composition according to any one of [1] to[5], further comprising an active material (D).

[7] The solid electrolyte composition according to any one of [1] to[6], further comprising a conductive auxiliary agent (E).

[8] The solid electrolyte composition according to any one of [1] to[7], in which the inorganic solid electrolyte (A) is a sulfide-basedinorganic solid electrolyte.

[9] A solid electrolyte-containing sheet that is formed of the solidelectrolyte composition according to any one of [1] to [8].

[10] A solid electrolyte-containing sheet comprising:

an inorganic solid electrolyte (A) having ion conductivity of a metalbelonging to Group 1 or Group 2 in the periodic table;

a binder (B); and

a solvent (C1),

in which the binder (B) includes a first binder (B1) that precipitatesby a centrifugal separation process and a second binder (B2) that doesnot precipitate by the centrifugal separation process, the centrifugalseparation process being performed in the solvent (C1) at a temperatureof 25° C. at a centrifugal force of 610000 G for 1 hour, and

a content X of the first binder (B1) and a content Y of the secondbinder (B2) satisfy the following expression by mass,0.10≤Y/(X+Y)≤0.80.

[11] An electrode sheet for an all-solid state secondary batterycomprising the solid electrolyte-containing sheet according to [9] or[10].

[12] An all-solid state secondary battery comprising:

a positive electrode active material layer;

a negative electrode active material layer; and

a solid electrolyte layer that is interposed between the positiveelectrode active material layer and the negative electrode activematerial layer,

in which at least one of the positive electrode active material layer,the negative electrode active material layer, or the solid electrolytelayer is the solid electrolyte-containing sheet according to [9] or[10].

[13] A method of manufacturing a solid electrolyte-containing sheetcomprising applying the solid electrolyte composition according to anyone of [1] to [8] to a substrate to form a coating film.

[14] The method of manufacturing a solid electrolyte-containing sheetaccording to [13] further comprising drying the coating film.

[15] A method of manufacturing an all-solid state secondary batterycomprising the method of manufacturing a solid electrolyte-containingsheet according to [13] or [14].

By using the solid electrolyte composition according to the presentinvention as a material for forming a layer, a layer in which theoccurrence of a defect (chipping, cracking, fracturing or peeling) issuppressed even after bending with a smaller bend radius can be formed,and a layer having high ion conductivity even after the bending can beformed.

In the solid electrolyte-containing sheet, the electrode sheet for anall-solid state secondary battery, and the all-solid state secondarybattery according to the present invention, the occurrence of a defectduring bending with a smaller bend radius is suppressed, and excellention conductivity can be exhibited even after the bending.

With the method of manufacturing a solid electrolyte-containing sheetand the method of manufacturing an all-solid state secondary batteryaccording to the present invention, the above-described solidelectrolyte-containing sheet and the all-solid state secondary batteryaccording to the present invention can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical cross-sectional view schematically illustrating anall-solid state secondary battery according to a preferred embodiment ofthe present invention.

FIG. 2 is a vertical cross-sectional view schematically illustrating anall-solid state secondary battery (coin battery) prepared in Examples.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the description of the present invention, numerical rangesrepresented by “to” include numerical values before and after “to” aslower limit values and upper limit values.

[Solid Electrolyte Composition]

A solid electrolyte composition according to an embodiment of thepresent invention comprises: an inorganic solid electrolyte having ionconductivity of a metal belonging to Group 1 or Group 2 in the periodictable; a binder (B); and a dispersion medium (C).

The binder (B) includes, at a specific ratio, a binder that precipitatesby an ultracentrifugal separation process in a state where it isincluded in the dispersion medium (C) and a binder (that remains in asupernatant) that does not precipitate by the ultracentrifugalseparation process. That is, the binder (B) includes a binder (firstbinder (B1)) that precipitates after a centrifugal separation process(ultracentrifugal separation process) and a binder (second binder (B2))that remains in a supernatant without precipitating after thecentrifugal separation process, the centrifugal separation process beingperformed at a temperature of 25° C. at a centrifugal force of 610000 Gfor 1 hour in a state where the binder (B) is dispersed or dissolved inthe dispersion medium (C).

In the solid electrolyte composition according to the embodiment of thepresent invention, a relationship between a content X of the firstbinder (B1) and a content Y of the second binder (B2) satisfies thefollowing expression by mass.0.10≤Y/(X+Y)≤0.80.

The solid electrolyte composition according to the embodiment of thepresent invention may include an active material (D) described below asdesired. In addition, the solid electrolyte composition may include aconductive auxiliary agent (E). The solid electrolyte compositionincluding the above-described components can be used as a material forforming an electrode active material layer.

A mixed state of the respective components in the solid electrolytecomposition according to the embodiment of the present invention is notparticularly limited as long as the solid electrolyte compositionincludes the respective components defined by the present invention. Itis preferable that the solid electrolyte composition according to theembodiment of the present invention is in a state where the respectivecomponents are substantially uniformly dispersed in the dispersionmedium at least before or during use.

In the solid electrolyte composition according to the embodiment of thepresent invention, the binder (B) have the above-described configurationand can allow a layer (a solid electrolyte layer, a negative electrodeactive material layer, or a positive electrode active material layer) inwhich an increase in electrical resistance is suppressed to be formedwhile effectively improving binding properties between solid particlesforming the composition. In the layer that is formed of the solidelectrolyte composition according to the embodiment of the presentinvention, the occurrence of a defect even after bending with a smallerbend radius is suppressed, and excellent ion conductivity can beexhibited even after the bending. Accordingly, in a manufacturing stepof a solid electrolyte-containing sheet, an electrode sheet for anall-solid state secondary battery, and all-solid state secondarybattery, a manufacturing form thereof, and the like, even in a casewhere a force such as bending or a pressure is applied, the occurrenceof a defect in the layer is suppressed, and excellent ion conductivitycan be stably exhibited.

The respective components that form or may form the solid electrolytecomposition according to the embodiment of the present invention will bedescribed.

<Inorganic Solid Electrolyte (A)>

In the present invention, the inorganic solid electrolyte is aninorganic solid electrolyte, and the solid electrolyte refers to asolid-form electrolyte capable of migrating ions therein. The inorganicsolid electrolyte is clearly distinguished from organic solidelectrolytes (polymer electrolytes such as polyethylene oxide (PEO) andorganic electrolyte salts such as lithiumbis(trifluoromethanesulfonyl)imide (LiTFSI)) since the inorganic solidelectrolyte does not include any organic substance as a principal ionconductive material. In addition, the inorganic solid electrolyte issolid in a steady state and thus, typically, is not dissociated orliberated into cations and anions. Due to this fact, the inorganic solidelectrolyte is also clearly distinguished from inorganic electrolytesalts of which cations and anions are dissociated or liberated inelectrolytic solutions or polymers (LiPF₆, LiBF₄, LiFSI, LiCl, and thelike). The inorganic solid electrolyte is not particularly limited aslong as it has ion conductivity of a metal belonging to Group 1 or Group2 in the periodic table and generally does not have electronconductivity.

In the present invention, the inorganic solid electrolyte has ionconductivity of a metal belonging to Group 1 or Group 2 in the periodictable. The inorganic solid electrolyte can be appropriately selectedfrom solid electrolyte materials to be applied to this kind of productsand used. Representative examples of the inorganic solid electrolyteinclude (i) a sulfide-based inorganic solid electrolyte and (ii) anoxide-based inorganic solid electrolyte. From the viewpoint of a highion conductivity and easiness in joining interfaces between particles, asulfide-based inorganic solid electrolyte is preferable.

In a case where an all-solid state secondary battery according to theembodiment of the present invention is an all-solid state lithium ionsecondary battery, the inorganic solid electrolyte preferably has ionconductivity of lithium ions.

(i) Sulfide-Based Inorganic Solid Electrolyte

The sulfide-based inorganic solid electrolyte is preferably a compoundthat contains a sulfur atom (S), has ion conductivity of a metalbelonging to Group 1 or Group 2 in the periodic table, and haselectron-insulating properties. The sulfide-based inorganic solidelectrolyte is preferably an inorganic solid electrolyte that containsat least Li, S, and P as elements and has lithium ion conductivity.However, the sulfide-based inorganic solid electrolyte may includeelements other than Li, S, and P depending on the purposes or cases.

Examples of the sulfide-based inorganic solid electrolyte include alithium ion-conductive sulfide-based inorganic solid electrolytesatisfying a composition represented by the following Formula (I).L _(a1) M _(b1) P _(c1) S _(d1) A _(c1)  Formula (I)

In the formula, L represents an element selected from Li, Na, or K andis preferably Li. M represents an element selected from B, Zn, Sn, Si,Cu, Ga, Sb, Al, or Ge. A represents an element selected from 1, Br, Cl,or F. a1 to e1 represent the compositional ratios among the respectiveelements, and a1:b1:c1:d1:e1 satisfies 1 to 12:0 to 5:1:2 to 12:0 to 10.a1 is preferably 1 to 9 and more preferably 1.5 to 7.5. b1 is preferably0 to 3 and more preferably 0 to 1. d1 is preferably 2.5 to 10 and morepreferably 3.0 to 8.5. e1 is preferably 0 to 5 and more preferably 0 to3.

The compositional ratios among the respective elements can be controlledby adjusting the ratios of raw material compounds blended to manufacturethe sulfide-based inorganic solid electrolyte as described below.

The sulfide-based inorganic solid electrolyte may be non-crystalline(glass) or crystallized (made into glass ceramic) or may be onlypartially crystallized. For example, it is possible to use Li—P—S-basedglass containing Li, P, and S or Li—P—S-based glass ceramic containingLi, P, and S.

The sulfide-based inorganic solid electrolytes can be manufactured by areaction of at least two raw materials of, for example, lithium sulfide(Li₂S), phosphorus sulfide (for example, diphosphoruspentasulfide(P₂S₅)), a phosphorus single body, a sulfur single body, sodium sulfide,hydrogen sulfide, lithium halides (for example, LiI, LiBr, and LiCl), orsulfides of an element represented by M (for example, SiS₂, SnS, andGeS₂).

The ratio between Li₂S and P₂S₅ in Li—P—S-based glass and Li—P—S-basedglass ceramic is preferably 60:40 to 90:10 and more preferably 68:32 to78:22 in terms of the molar ratio between Li₂S:P₂S₅. By mixing Li₂S andP₂S₅ at a ratio in the above-described range, a sulfide-based inorganicsolid electrolyte having a high lithium ion conductivity can beobtained. Specifically, the lithium ion conductivity can be preferablyset to 1×10⁴ S/cm or more and more preferably set to 1×10⁻³ S/cm ormore. The upper limit is not particularly limited, but realistically1×10⁻¹ S/cm or less.

As specific examples of the sulfide-based inorganic solid electrolytes,combination examples of raw materials will be described below. Examplesthereof include Li₂S—P₂S₅, Li₂S—P₂S₅—LiCl, Li₂S—P₂S₅—H₂S,Li₂S—P₂S₅—H₂S—LiCl, Li₂S—LiI—P₂S₅, Li₂S—LiI—Li₂O—P₂S₅, Li₂S—LiBr—P₂S₅,Li₂S—Li₂O—P₂S₅, Li₂S—Li₃PO₄—P₂S₅, Li₂S—P₂S₅—P₂O₅, Li₂S—P₂S₅—SiS₂,Li₂S—P₂S₅—SiS₂—LiCl, Li₂S—P₂S₅—SnS, Li₂S—P₂S₅—Al₂S₃, Li₂S—GeS₂,Li₂S—GeS₂—ZnS, Li₂S—Ga₂S₃, Li₂S—GeS₂—Ga₂S₃, Li₂S—GeS₂—P₂S₅,Li₂S—GeS₂—Sb₂S₅, Li₂S—GeS₂—Al₂S₃, Li₂S—SiS₂, Li₂S—Al₂S₃,Li₂S—SiS₂—Al₂S₃, Li₂S—SiS₂—P₂S₅, Li₂S—SiS₂—P₂S₅—LiI, Li₂S—SiS₂—LiI,Li₂S—SiS₂—Li₄SiO₄, Li₂S—SiS₂—Li₃PO₄, and Li₁₀GeP₂S₁₂. Mixing ratios ofthe respective raw materials do not matter. Examples of a method forsynthesizing the sulfide-based inorganic solid electrolyte materialusing the above-described raw material compositions include anamorphization method. Examples of the amorphization method include amechanical milling method, a solution method, and a melting quenchingmethod. With the amorphization method, treatments at a normaltemperature can be performed, and manufacturing steps can be simplified.

(ii) Oxide-Based Inorganic Solid Electrolyte

The oxide-based inorganic solid electrolyte is preferably a compoundthat contains an oxygen atom (O), has ion conductivity of a metalbelonging to Group 1 or Group 2 in the periodic table, and haselectron-insulating properties.

Specific examples of the compound include: Li_(xa)La_(ya)TiO₃(0.3≤xa≤0.7 and 0.3≤ya≤0.7) (LLT); Li_(xb)La_(yb)Zr_(zb)M^(bb)_(mb)O_(nb) (M^(bb) represents at least one element selected from Al,Mg, Ca, Sr, V, Nb, Ta, Ti, Ge, In, or Sn, 5≤xb≤10, 1≤yb≤4, 1≤zb≤4,0≤mb≤2, and 5≤nb≤20); Li_(xc)B_(yc)M^(cc) _(zc)O_(nc) (M^(cc) representsat least one element selected from C, S, Al, Si, Ga, Ge, In, or Sn,0≤xc≤5, 0≤yc≤1, 0≤zc≤1, and 0≤nc≤6);Li_(xd)(Al,Ga)_(yd)(Ti,Ge)_(zd)Si_(ad)P_(md)O_(nd) (1≤xd≤3, 0≤yd≤1,0≤zd≤2, 0≤ad≤1, 1≤md≤7, and 3≤nd≤13); Li_((3−2xe))M^(ee) _(xe)D^(ee)O(0≤xe≤0.1, M^(ee) represents a divalent metal atom, and D^(ee)represents a halogen atom or a combination of two or more halogenatoms); Li_(xf)Si_(yf)O_(xf) (1≤xf≤5, 0≤yf≤3, and 1≤zf≤10);Li_(xg)S_(yg)O_(zg) (1≤xg≤3, 0≤yg≤2, and 1≤zg≤10); Li₃BO₃—Li₂SO₄;Li₂O—B₂O₃—P₂O₅; Li₂O—SiO₂; Li₆BaLa₇Ta₇O₁₂; Li₃PO_((4−3/2w))N_(w) (w<1);Li_(3.5)Zn_(0.25)GeO₄ having a lithium super ionic conductor(LISICON)-type crystal structure; La_(0.55)Li_(0.35)TiO₃ having aperovskite-type crystal structure; LiTi₂P₃O₁₂ having a natrium superionic conductor (NASICON)-type crystal structure;Li_(1+xh+yh)(Al,Ga)_(xh)(Ti,Ge)_(2−xh)Si_(yh)P_(3−yh)—O₁₂ (0≤xh≤1, and0≤yh≤1); and Li₇La₃Zr₂O₁₂ (LLZ) having a garnet-type crystal structure.In addition, phosphorus compounds containing Li, P, and O are alsodesirable. Examples thereof include lithium phosphate (Li₃PO₄) and LiPONin which some of oxygen atoms in lithium phosphate are substituted withnitrogen atoms, LiPOD¹ (D¹ is at least one element selected from Ti, V,Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ru, Ag, Ta, W, Pt, Au, or the like).It is also possible to preferably use LiA¹ON (A¹ represents at least oneelement selected from Si, B, Ge, Al, C, Ga, or the like) and the like.

The inorganic solid electrolyte is preferably in the form of particles.In this case, the particle size of the inorganic solid electrolyte isnot particularly limited. From the viewpoints of ion conductivity,workability, and interface formability, the particle size of theinorganic solid electrolyte is preferably 0.01 μm or more, morepreferably 0.2 μm or more, and still more preferably 0.3 μm or more. Inaddition, the particle size of the inorganic solid electrolyte ispreferably 100 μm or less, more preferably 50 μm or less, still morepreferably 20 μm or less, still more preferably 4 μm or less, and stillmore preferably 2 μm or less.

The particle size of the inorganic solid electrolyte particles refer tothe average particle size and can be determined as described below.

The inorganic solid electrolyte particles are diluted and adjusted to 1mass % of a dispersion liquid by using water (heptane in a case wherethe inorganic solid electrolyte is unstable in water) in a 20 mL samplebottle. The diluted dispersion specimen is irradiated with 1 kHzultrasonic waves for 10 minutes and is then immediately used fortesting. The volume average particle size is obtained by acquiring data50 times using this dispersion liquid specimen, a laserdiffraction/scattering particle size distribution analyzer LA-920 (tradename, manufactured by Horiba Ltd.), and a quartz cell for measurement ata temperature of 25° C. Other detailed conditions and the like can befound in JIS Z8828: 2013 “Particle Size Analysis-Dynamic LightScattering” as necessary. For each level, five samples are prepared andthe average value thereof is adopted.

As the inorganic solid electrolyte, one kind may be used alone, or twoor more kinds may be used in combination.

The content of the inorganic solid electrolyte in the solid electrolytecomposition is not particularly limited. From the viewpoints of reducingthe interface resistance during use in an all-solid state secondarybattery and maintaining the reduced interface resistance, the content ofthe inorganic solid electrolyte is preferably 5 parts by mass or more,more preferably 10 parts by mass or more, and still more preferably 20parts by mass or more with respect to 100 parts by mass of the solidcomponents in the composition. In addition, from the same viewpoints,the content of the inorganic solid electrolyte is preferably 99.9 partsby mass or less, more preferably 99.5 parts by mass or less, and stillmore preferably 99 parts by mass or less with respect to 100 parts bymass of the solid components in the composition.

In the present invention, the solid content (solid component) refers tocomponents that neither volatilize nor evaporate and disappear in a casewhere the solid electrolyte composition is dried at 120° C. for 6 hoursin a nitrogen atmosphere at a pressure of 1 mmHg. Typically, the solidcontent refers to components other than a dispersion medium describedbelow.

<Binder (B)>

The solid electrolyte composition according to the embodiment of thepresent invention includes the binder (B). The binder (B) in thecomposition can be formed of various polymers. The binder (B) mayinclude a particle polymer or a non-particle polymer. As describedbelow, the solid electrolyte composition according to the embodiment ofthe present invention includes, at a specific ratio, a binder thatbecomes a precipitate component after an ultracentrifugal separationprocess under a specific condition and a binder that becomes asupernatant component after the ultracentrifugal separation process.

First, the polymer that may form the binder (B) will be described. Thebinder (B) can be formed of, for example, an organic resin describedbelow.

(Fluorine-Containing Resin)

Examples of a fluorine-containing resin include polytetrafluoroethylene(PTFE), polyvinylidene difluoride (PVdF), and a copolymer (PVdF-HFP) ofpolyvinylidene difluoride and hexafluoropropylene.

(Hydrocarbon-Based Thermoplastic Resin)

Examples of a hydrocarbon-based thermoplastic resin includepolyethylene, polypropylene, styrene-butadiene rubber (SBR),hydrogenated styrene-butadiene rubber (HSBR), butyl ene rubber,acrylonitrile-butadiene rubber, polybutadiene, and polyisoprene.

((Meth)Acrylic Resin)

Examples of a (meth)acrylic resin include various (meth)acrylicmonomers, (meth)acrylamide monomers, and copolymers of two or moremonomers thereof.

In addition, copolymers of vinyl monomers are also be suitably used.Examples of the copolymers include a copolymer of methyl (meth)acrylateand styrene, a copolymer of methyl (meth)acrylate and acrylonitrile, anda copolymer of butyl (meth)acrylate, acrylonitrile, and styrene.However, the copolymers are not limited to these examples. In thepresent specification, the copolymer may be any one of a statisticcopolymer or a periodic copolymer and is preferably a random copolymer.

(Other Resins)

Examples of other resins include a polyurethane resin, a polyurea resin,a polyamide resin, a polyimide resin, a polyester resin, a polyetherresin, a polycarbonate resin, and a cellulose derivative resin.

Among these, a fluorine-containing resin, a hydrocarbon-basedthermoplastic resin, a (meth)acrylic resin, a polyurethane resin, apolycarbonate resin, or a cellulose derivative resin is preferable, anda (meth)acrylic resin or a polyurethane resin is more preferable fromthe viewpoint of high affinity to the inorganic solid electrolyte, highflexibility of the resin itself, and strong binding properties with thesolid particles.

The above-described various resins are commercially available. Inaddition, the binder resin particles or the polymer forming the binderresin particles can also be prepared using an ordinary method.

The above-described organic resin is merely exemplary, and the binder(B) according to the embodiment of the present invention is not limitedto this configuration.

In the present invention, unless specified otherwise, the weight-averagemolecular weight of the polymer refers to the weight-average molecularweight in terms of standard polystyrene measured by gel permeationchromatography (GPC). The measured value is a value measured under thefollowing condition. In this case, an appropriate eluent can beappropriately selected and used depending on the kind of the polymer.

(Conditions)

Column: A column obtained by connecting TOSOH TSKgel Super HZM-H (tradename), TOSOH TSKgel Super HZ4000 (trade name), and TOSOH TSKgel SuperHZ2000 (trade name)

Carrier: tetrahydrofuran

Measurement temperature: 40° C.

Carrier flow rate: 1.0 mL/min

Sample concentration: 0.1 mass %

Detector: refractive index (RI) detector

That is, the binder (B) included in the solid electrolyte compositionaccording to the embodiment of the present invention includes a binder(first binder (B1)) that precipitates after a centrifugal separationprocess and a binder (second binder (B2)) that remains in a supernatantwithout precipitating after the centrifugal separation process at aspecific ratio described below, the centrifugal separation process(hereinafter, simply referred to as “ultracentrifugal separationprocess”) being performed at a temperature of 25° C. at a centrifugalforce of 610000 G for 1 hour in a state where the binder (B) isdispersed or dissolved in the dispersion medium described below formingthe solid electrolyte composition (a part thereof may be dissolved).After the ultracentrifugal separation process, the content of the binderin the dispersion medium is 0.1 to 10 mass %. Within the above-describedrange of the content, even in a case where the content of the bindervaries, a phenomenon in which the precipitate component is present in asupernatant or the supernatant component is converted into theprecipitate component does not occur in practice. In addition, thedetermination of the physical properties of the binder based on theultracentrifugal separation process is performed in a state where onlythe binder is dispersed or dissolved in the dispersion medium.

In the solid electrolyte composition according to the embodiment of thepresent invention, a relationship between the content X of the firstbinder (B1) and the content Y of the second binder (B2) satisfies thefollowing expression by mass.0.10≤Y/(X+Y)≤0.80

That is, a proportion of the polymer that is present in a supernatantwithout precipitating after the ultracentrifugal separation process inthe polymer forming the binder (B) included in the solid electrolytecomposition is 10 to 80 mass %. In other words, a proportion of thepolymer that is dissolved in the dispersion medium and/or is present inthe dispersion medium as resin fine particles having a small particlesize after the ultracentrifugal separation process in the polymerforming the binder (B) is 10% to 80 mass %.

On the other hand, the first binder (B1) is typically present in thedispersion medium as resin fine particles.

In the solid electrolyte composition according to the embodiment of thepresent invention, the first binder (B1) and the second binder (B2) maybe present independently or may be present in a state where theyinteract with each other (adsorption or the like).

It is preferable that the relationship between the content X of thefirst binder (B1) and the content Y of the second binder (B2) satisfiesthe following expression by mass.0.10≤Y/(X+Y)≤0.60

It is more preferable that the relationship satisfies the followingexpression.0.10≤Y/(X+Y)≤0.50

It is still more preferable that the relationship satisfies thefollowing expression.0.15≤Y/(X+Y)≤0.45

It is still more preferable that the relationship satisfies thefollowing expression.0.20≤Y/(X+Y)≤0.40

In a layer that is formed of the solid electrolyte composition in whichthe binder is dissolved in the dispersion medium, substantially all thesolid particle surfaces are covered with the binder. In this state,binding properties between the solid particles can be improved. However,typically, the interface resistance increases, and the ion conductivitydecreases. Therefore, in the layer that is formed by allowing the binderto be present in the form of particles using the resin that is notdissolved in the dispersion medium as described in JP2015-088486A, thetechnique of suppressing an increase in interface resistance whileimproving binding properties between the solid particles is reported.

On the other hand, the solid electrolyte composition according to theembodiment of the present invention includes not only a specific amountof the first binder (B1) that is insoluble in the dispersion medium andbecomes the precipitate component after the ultracentrifugal separationprocess but also a specific amount of the second binder (B2) that isdissolved in the dispersion medium or is present in the form ofparticles having a small particle size and becomes the supernatantcomponent after the ultracentrifugal separation process. That is, thisidea is simply different from a technique in which a fine particlepolymer is used as a binder. As a result, the binding properties betweenthe solid particles can be highly improved, and an increase in interfaceresistance can be effectively suppressed. As a result, a layer in whichthe occurrence of a defect even after bending with a smaller bend radiusis suppressed and ion conductivity is excellent can be formed.

(First Binder (B1))

The first binder (B1) exhibits the above-described behavior after theultracentrifugal separation process. In the solid electrolytecomposition according to the embodiment of the present invention, thefirst binder (B1) is typically in the form of particles. The particlesize of the first binder (B1) is preferably 10 to 10000 nm, morepreferably 50 to 1000 nm, and still more preferably 100 to 500 nm. Theparticle size of the binder particles refers to an average primaryparticle size. The measurement of the average particle size of thebinder particles can be determined using the same method as the methodof measuring the particle size of the inorganic solid electrolyte. In acase where the particle size of the binder particles is less than orequal to a measurement limit of the above-described device, the particlesize is measured using a transmission electron microscope (TEM) afteroptionally drying and hardening the binder resin particles.

From the viewpoint of improving binding properties between the solidparticles, the number-average molecular weight of the polymer formingthe first binder (B1) is preferably 10000 to 1000000 and more preferably30000 to 500000. An aspect in which the first binder (B1) is formed of acrosslinked product of a polymer having a weight-average molecularweight in the above-described range is also preferable.

(Second Binder (B2))

The second binder (B2) exhibits the above-described behavior after theultracentrifugal separation process. The second binder (B2) is a polymerthat is soluble in the dispersion medium forming the composition or ispresent in the form of particles having a small particle size in thedispersion medium forming the composition. In addition, the secondbinder (B2) is present in a state where it interacts (for example,adsorption) with the first binder (B1).

From the viewpoint of improving initial adhesiveness between the solidparticles, the number-average molecular weight of the polymer formingthe second binder (B2) is preferably 1000 to 500000 and more preferably3000 to 100000.

The glass transition temperature (Tg) of the polymer forming the secondbinder (B2) is preferably −50° C. to 10° C. and more preferably −30° C.to 0° C. In a case where Tg of the second binder (B2) is in theabove-described preferable range, the wettability on the active materialor the inorganic solid electrolyte can be further improved.

Tg is measured using a dry sample with a differential scanningcalorimeter “X-DSC7000” (trade name, manufactured by SII NanoTechnologyInc.) under the following conditions. The measurement is performed twiceusing the same sample, and the result of the second measurement isadopted.

Atmosphere in measuring chamber: nitrogen (50 mL/min)

Temperature increase rate: 5° C./min

Measurement start temperature: −100° C.

Measurement end temperature: 200° C.

Sample pan: aluminum pan

Mass of measurement sample: 5 mg

Calculation of Tg: Tg is calculated by rounding off the decimal point ofan intermediate temperature between a declination start point and adeclination end point in a DSC chart

In the solid electrolyte composition according to the embodiment of thepresent invention, it is preferable that a relationship between thecontent Y of the second binder (B2) and a content Z of the inorganicsolid electrolyte (A) satisfies the following expression by mass ratio.0.001≤Y/(Y+Z)≤0.1

The content Z refers to a content Z1 of the inorganic solid electrolyte(A) in a case where the solid electrolyte composition does not includethe active material (D), and refers to a sum Z2 of the content of theinorganic solid electrolyte (A) and a content of the active material (D)in a case where the solid electrolyte composition includes the activematerial (D).

By the relationship satisfying the above-described expression, anincrease in interface resistance between particles of the inorganicsolid electrolyte or between the inorganic solid electrolyte and theactive material is further suppressed, and higher ion conductivity canbe realized.

It is preferable that the relationship between the content Y of thesecond binder (B2) and the content Z of the inorganic solid electrolyte(A) (that refers to the sum of the content of the inorganic solidelectrolyte (A) and the content of the active material (D) in a casewhere the solid electrolyte composition includes the active material(D)) satisfies the following expression.0.002≤Y/(Y+Z)≤0.07

It is more preferable that the relationship satisfies the followingexpression.0.003≤Y/(Y+Z)≤0.05

It is still more preferable that the relationship satisfies thefollowing expression.0.003≤Y/(Y+Z)≤0.03

From the viewpoints of reducing the interface resistance during use inthe all-solid state secondary battery and maintaining the reducedinterface resistance, the total content of the first binder (B1) and thesecond binder (B2) in the solid electrolyte composition according to theembodiment of the present invention is preferably 0.01 parts by mass ormore, more preferably 0.1 parts by mass or more, and still morepreferably 1 parts by mass or more with respect to 100 parts by mass ofthe solid components. In addition, from the viewpoint of batteryperformance, the total content is preferably 20 parts by mass or less,more preferably 10 parts by mass or less, and still more preferably 5parts by mass or less.

The binder (B) included in the solid electrolyte composition accordingto the embodiment of the present invention may be formed of one polymerhaving the same component ratio as that of the kind of the component. Inthis case, for example, by using a polymer having a wide molecularweight distribution, the polymer is separated into the precipitatecomponent and the supernatant component after the ultracentrifugalseparation process. Typically, the binder (B) includes two or morepolymers including different components (having different componentratios). It is preferable that the binder (B) includes 2 to 10 polymersincluding different components, it is more preferable that the binder(B) includes 2 to 5 polymers including different components, and it isstill more preferable that the binder (B) includes 2 to 4 polymersincluding different components.

<Active Material (D)>

The solid electrolyte composition according to the embodiment of thepresent invention may include the active material capable ofintercalating and deintercalating ions of a metal element belonging toGroup 1 or Group 2 in the periodic table. Examples of the activematerial include a positive electrode active material and a negativeelectrode active material. The solid electrolyte composition includingthe active material can be suitably used for forming an electrode activematerial layer of an all-solid state secondary battery.

The shape of the active material is not particularly limited, but ispreferably a particle shape. In addition, the particle size of theactive material is not particularly limited as long as it satisfies theabove-described particle size. From the viewpoint of improvingdispersibility, improving the contact area between the solid particles,and reducing the interfacial reactivity, the particle size of the activematerial is preferably 0.1 μm or more, more preferably 1 μm or more, andstill more preferably 2 μm or more. In addition, the particle size ofthe active material is preferably 20 μm or less, more preferably 10 μmor less, and still more preferably 5 urn or less. The particle size ofthe active material refers to an average particle size and can bedetermined using the same method as that of the particle size of theinorganic solid electrolyte. In a case where the particle size of theactive material is less than or equal to a measurement limit of theparticle size analyzer, the particle size is measured using atransmission electron microscope (TEM) after optionally drying andhardening the active material.

Examples of the active material include a positive electrode activematerial and a negative electrode active material. In particular, ametal oxide (preferably a transition metal oxide) that is the positiveelectrode active material, a metal oxide that is the negative electrodeactive material, or metal such as Sn, Si, Al, or In capable of formingan alloy with lithium is preferable.

In the present invention, the solid electrolyte composition includingthe active material (the positive electrode active material or thenegative electrode active material) will be referred to as an electrodecomposition (a positive electrode composition or a negative electrodecomposition).

(Positive Electrode Active Material)

The positive electrode active material is preferably capable ofreversibly intercalating and deintercalating lithium ions. Theabove-described material is not particularly limited as long as thematerial has the above-described characteristics and may be transitionmetal oxides, organic substances, elements capable of being complexedwith Li such as sulfur, complexes of sulfur and metal, or the like.

Among these, as the positive electrode active material, transition metaloxides are preferably used, and transition metal oxides having atransition metal element M^(a) (one or more elements selected from Co,Ni, Fe, Mn, Cu, and V) are more preferable. In addition, an elementM^(b) (an element of Group 1 (Ia) of the metal periodic table other thanlithium, an element of Group 2 (IIa), or an element such as Al, Ga, In,Ge, Sn, Pb, Sb, Bi, Si, P, or B) may be mixed into this transition metaloxide. The amount of the M^(b) mixed is preferably 0 to 30 mol % of theamount (100 mol %) of the transition metal element M^(a). It is morepreferable that the transition metal oxide is synthesized by mixing theabove components such that a molar ratio Li/M^(a) is 0.3 to 2.2.

Specific examples of the transition metal oxides include transitionmetal oxides having a layered rock salt structure (MA), transition metaloxides having a spinel-type structure (MB), lithium-containingtransition metal phosphate compounds (MC), lithium-containing transitionmetal halogenated phosphate compounds (MD), and lithium-containingtransition metal silicate compounds (ME).

Specific examples of the transition metal oxides having a layered rocksalt structure (MA) include LiCoO₂ (lithium cobalt oxide [LCO]), LiNi₂O₂(lithium nickel oxide) LiNi_(0.85)Co_(0.10)Al_(0.05)O₂ (lithium nickelcobalt aluminum oxide [NCA]), LiNi_(1/3)CO_(1/3)Mn_(1/3)O₂ (lithiumnickel manganese cobalt oxide [NMC]), and LiNi_(0.5)Mn_(0.5)O₂ (lithiummanganese nickel oxide).

Specific examples of the transition metal oxides having a spinel-typestructure (MB) include LiMn₂O₄ (LMO), LiCoMnO₄, Li₂FeMn₃O₈, Li₂CuMn₃O₈,Li₂CrMn₃O₈, and Li₂NiMn₃O₈.

Examples of the lithium-containing transition metal phosphate compounds(MC) include olivine-type iron phosphate salts such as LiFePO₄ andLi₃Fe₂(PO₄)₃, iron pyrophosphates such as LiFeP₂O₇, and cobaltphosphates such as LiCoPO₄, and monoclinic nasicon-type vanadiumphosphate salt such as Li₃V₂(PO₄)₃ (lithium vanadium phosphate).

Examples of the lithium-containing transition metal halogenatedphosphate compounds (MD) include iron fluorophosphates such asLi₂FePO₄F, manganese fluorophosphates such as Li₂MnPO₄F, cobaltfluorophosphates such as Li₂CoPO₄F.

Examples of the lithium-containing transition metal silicate compounds(ME) include Li₂FeSiO₄, Li₂MnSiO₄, and Li₂CoSiO₄.

In the present invention, the transition metal oxides having a layeredrock salt structure (NIA) is preferable, and LCO or NMC is morepreferable.

In order to allow the positive electrode active material to have adesired particle size, an ordinary pulverizer or classifier may be used.Positive electrode active materials obtained using a calcination methodmay be used after being washed with water, an acidic aqueous solution,an alkaline aqueous solution, or an organic solvent.

As the positive electrode active material, one kind may be used alone,or two or more kinds may be used in combination.

In the case of forming a positive electrode active material layer, themass (mg) of the positive electrode active material per unit area (cm²)of the positive electrode active material layer (weight per unit area)is not particularly limited. The mass can be appropriately determineddepending on the designed battery capacity.

The content of the positive electrode active material in the solidelectrolyte composition is not particularly limited, but is preferably10 to 95 parts by mass, more preferably 30 to 90 parts by mass, stillmore preferably 50 to 85 parts by mass, and still more preferably 55 to80 parts by mass with respect to 100 parts by mass of the solid content.

(Negative Electrode Active Material)

The negative electrode active material is preferably capable ofreversibly intercalating and deintercalating lithium ions. Theabove-described material is not particularly limited as long as thematerial has the above-described characteristics, and examples thereofinclude carbonaceous materials, metal oxides such as tin oxide, siliconoxide, metal composite oxides, a lithium single body, lithium alloyssuch as lithium aluminum alloys, metals capable of forming alloys withlithium such as Sn, Si, Al, and In and the like. Among these, acarbonaceous material or a lithium composite oxide is preferably usedfrom the viewpoint of reliability. In addition, the metal compositeoxide is preferably capable of intercalating and deintercalatinglithium. The material is not particularly limited, but preferablyincludes titanium and/or lithium as a constituent element from theviewpoint of high current density charging-discharging characteristics.

The carbonaceous material which is used as the negative electrode activematerial is a material substantially containing carbon. Examples thereofinclude petroleum pitch, carbon black such as acetylene black (AB),graphite (natural graphite, artificial graphite such as vapor-growngraphite), and carbonaceous material obtained by firing a variety ofsynthetic resins such as polyacrylonitrile (PAN)-based resins orfurfuryl alcohol resins. Furthermore, examples thereof also include avariety of carbon fibers such as PAN-based carbon fibers,cellulose-based carbon fibers, pitch-based carbon fibers, vapor-growncarbon fibers, dehydrated polyvinyl alcohol (PVA)-based carbon fibers,lignin carbon fibers, vitreous carbon fibers, and activated carbonfibers, mesophase microspheres, graphite whisker, and tabular graphite.

The metal oxides and the metal composite oxides being applied as thenegative electrode active material are particularly preferably amorphousoxides, and furthermore, chalcogenides which are reaction productsbetween a metal element and an element belonging to Group 16 in theperiodic table are also preferably used. “Amorphous” described hereinrepresents an oxide having a broad scattering band with a peak in arange of 20° to 40° in terms of 2θ when measured by an X-ray diffractionmethod using CuKα rays, and the oxide may have a crystal diffractionline.

In a compound group consisting of the amorphous oxides and thechalcogenides, amorphous oxides of metalloid elements and chalcogenidesare more preferred, and elements belonging to Groups 13 (IIIB) to 15(VB) of the periodic table, oxides consisting of one element or acombination of two or more elements of Al, Ga, Si, Sn, Ge, Pb, Sb, andBi, and chalcogenides are particularly preferable. Specific examples ofpreferred amorphous oxides and chalcogenides include Ga₂O₃, SiO, GeO,SnO, SnO₂, PbO, PbO₂, Pb₂O₃, Pb₂O₄, Pb₃O₄, Sb₂O₃, Sb₂O₄, Sb₂O₈Bi₂O₃,Sb₂O₈Si₂O₃, Bi₂O₄, SnSiO₃, GeS, SnS, SnS₂, PbS, PbS₂, Sb₂S₃, Sb₂S₅, andSnSiS₃. In addition, these amorphous oxides may be composite oxides withlithium oxide, for example, Li₂SnO₂.

The negative electrode active material preferably contains a titaniumatom. More specifically, Li₄Ti₅O₁₂ (lithium titanium oxide [LTO]) ispreferable since the volume fluctuation during the intercalation anddeintercalation of lithium ions is small, and thus the high-speedcharging-discharging characteristics are excellent, and thedeterioration of electrodes is suppressed, whereby it becomes possibleto improve the service lives of lithium ion secondary batteries.

In the present invention, a Si-based negative electrode is alsopreferably applied. Generally, a Si negative electrode is capable ofintercalating a larger number of Li ions than a carbon negativeelectrode (graphite, acetylene black, or the like). That is, the amountof Li ions intercalated per unit mass increases. Therefore, it ispossible to increase the battery capacity. As a result, there is anadvantage that the battery driving duration can be extended.

In order to allow the negative electrode active material to have apredetermined particle size, an ordinary pulverizer or classifier may beused. For example, a mortar, a ball mill, a sand mill, a vibration ballmill, a satellite ball mill, a planetary ball mill, a swirling air flowjet mill, a sieve, or the like is preferably used. During thepulverization, wet pulverization of causing water or an organic solventsuch as methanol to coexist with the negative electrode active materialcan be optionally performed. In order to obtain a desired particle size,it is preferable to perform classification. A classification method isnot particularly limited, and a method using, for example, a sieve or anair classifier can be optionally used. The classification can be usedusing a dry method or a wet method.

The chemical formulae of the compounds obtained using a calcinationmethod can be measured by inductively coupled plasma (ICP) opticalemission spectroscopy, and can be calculated from the mass difference ofpowder before and after calcinating as a convenient method.

As the negative electrode active material, one kind may be used alone,or two or more kinds may be used in combination.

In the case of forming a negative electrode active material layer, themass (mg) of the negative electrode active material per unit area (cm²)in the negative electrode active material layer (weight per unit area)is not particularly limited. The mass can be appropriately determineddepending on the designed battery capacity.

The content of the negative electrode active material in the solidelectrolyte composition is not particularly limited, but is preferably10 to 80 parts by mass and more preferably 20 to 80 parts by mass withrespect to 100 parts by mass the solid content.

—Surface Coating of Active Material—

The surfaces of the positive electrode active material and the negativeelectrode active material may be coated with a separate metal oxide.Examples of the surface coating agent include metal oxides and the likecontaining Ti, Nb, Ta, W, Zr, Al, Si, or Li. Specific examples thereofinclude titanium oxide spinel, tantalum-based oxides, niobium-basedoxides, lithium and lithium niobate-based compounds, and specificexamples thereof include Li₄Ti₅O₁₂, Li₂Ti₂O₅, LiTaO₃, LiNbO₃, LiAlO₂,Li₂ZrO₃, Li₂WO₄, Li₂TiO₃, Li₂B₄O₇, Li₃PO₄, Li₂MoO₄, Li₃BO₃, LiBO₂,Li₂CO₃, Li₂SiO₃, SiO₂, TiO₂, ZrO₂, Al₂O₃, and B₂O₃.

In addition, a surface treatment may be carried out on the surfaces ofelectrodes including the positive electrode active material or thenegative electrode active material using sulfur, phosphorous, or thelike.

Furthermore, the particle surfaces of the positive electrode activematerial or the negative electrode active material may be treated withan actinic ray or an active gas (plasma or the like) before or after thecoating of the surfaces.

<Conductive Auxiliary Agent (E)>

The solid electrolyte composition according to the embodiment of thepresent invention may include a conductive auxiliary agent. Theconductive auxiliary agent is not particularly limited, and conductiveauxiliary agents that are known as ordinary conductive auxiliary agentscan be used. The conductive auxiliary agent may be, for example,graphite such as natural graphite or artificial graphite, carbon blacksuch as acetylene black, Ketjen black, or furnace black, irregularcarbon such as needle cokes, a carbon fiber such as a vapor-grown carbonfiber or a carbon nanotube, or a carbonaceous material such as grapheneor fullerene which are electron-conductive materials and also may bemetal powder or a metal fiber of copper, nickel, or the like, and aconductive polymer such as polyaniline, polypyrrole, polythiophene,polyacetylene, or a polyphenylene derivative may also be used.

In the present invention, in a case where the negative electrode activematerial and the conductive auxiliary agent are used in combination,among the above-described conductive auxiliary agents, a conductiveauxiliary agent that does not intercalate and deintercalate Li and doesnot function as a negative electrode active material during charging anddischarging of the battery is classified as the conductive auxiliaryagent. Therefore, among the conductive auxiliary agents, a conductiveauxiliary agent that can function as the negative electrode activematerial in the negative electrode active material layer during chargingand discharging of the battery is classified as a negative electrodeactive material not as a conductive auxiliary agent. Whether or not theconductive auxiliary agent functions as the negative electrode activematerial during charging and discharging of the battery is not uniquelydetermined but is determined based on a combination of the conductiveauxiliary agent with the negative electrode active material.

As the conductive auxiliary agent, one kind may be used alone, or two ormore kinds may be used in combination.

In particular, a carbon black such as acetylene black, Ketjen black, orfurnace black or a carbon fiber such as vapor-grown carbon fiber orcarbon nanotube is preferable.

The particle size of the conductive auxiliary agent is not particularlylimited and, from the viewpoints of forming a conductive path andobtaining the dispersibility of the solid electrolyte composition, ispreferably 0.001 μm or more, more preferably 0.01 μm or more, still morepreferably 0.05 μm or more, and still more preferably 0.1 μm or more. Inaddition, the upper limit is preferably 20 μm or less, more preferably 5μm or less, still more preferably 3 μm or less, still more preferably 2μm or less, and most preferably 0.5 μm or less.

The particle size of the conductive auxiliary agent refers to an averageparticle size and is measured using the same method as that of theparticle size of the inorganic solid electrolyte. In a case where theparticle size is less than or equal to a measurement limit of thedevice, the particle size is determined using a TEM after optionallydrying and hardening the conductive auxiliary agent.

The content of the conductive auxiliary agent in the solid electrolytecomposition is preferably 0.1 to 5 parts by mass and more preferably 0.5to 3 parts by mass with respect to 100 parts by mass of the solidcontent.

<Dispersion Medium (C)>

The solid electrolyte composition according to the embodiment of thepresent invention includes the dispersion medium as a medium fordispersing the inorganic solid electrolyte, the active material, theconductive auxiliary agent, the binder particles, and the like.

The dispersion medium is not particularly limited as long as it candisperse the respective components included in the solid electrolytecomposition according to the embodiment of the present invention, andexamples thereof include various organic solvents. Specific examples ofthe dispersion medium include an alcohol compound, an ether compound, anamide compound, an amine compound, a ketone compound, an aromaticcompound, an aliphatic compound, a nitrile compound, and an estercompound.

Examples of the alcohol compound include methyl alcohol, ethyl alcohol,1-propyl alcohol, 2-propyl alcohol, 2-butanol, ethylene glycol,propylene glycol, 1,6-hexanediol, cyclohexanediol, 1,3-butanediol, and1,4-butanediol.

Examples of the ether compound include alkylene glycols (triethyleneglycol and the like), alkylene glycol monoalkyl ethers (ethylene glycolmonomethyl ether and the like), alkylene glycol dialkyl ethers (ethyleneglycol dimethyl ether and the like), dialkyl ethers (diisopropyl ether,dibutyl ether, and the like), and cyclic ethers (tetrahydrofuran, anddioxane (including each of 1,2-, 1,3-, and 1,4-isomers), and the like).

Examples of the amide compound include N,N-dimethylformamide,N-methyl-2-pyrrolidone, 2-pyrrolidinone, 1,3-dimethyl-2-imidazolidinone,2-pyrrolidinone, s-caprolactam, formamide, N-methylformamide, acetamide,N-methylacetamide, N,N-dimethylacetamide, N-methylpropanamide, andhexamethylphosphorictriamide.

Examples of the amine compound include triethylamine,diisopropylethylamine, and tributylamine.

Examples of the ketone compound include acetone, methyl ethyl ketone,methyl isobutyl ketone, cyclopentanone, cyclohexanone, cycloheptanone,dipropyl ketone, dibutyl ketone, diisopropyl ketone, diisobutyl ketone,isobutyl propyl ketone, sec-butyl propyl ketone, pentyl propyl ketone,and butyl propyl ketone.

Examples of the aromatic compound include benzene, toluene, and xylene.

Examples of the aliphatic compound include hexane, heptane, octane,decane, cyclohexane, cyclooctane, decalin, paraffin, gasoline, naphtha,kerosene, and light oil.

Examples of the nitrile compound include acetonitrile, propionitrile,and isobutyronitrile.

Examples of the ester compound include ethyl acetate, butyl acetate,propyl acetate, propyl butyrate, isopropyl butyrate, butyl butyrate,isobutyl butyrate, butyl pentanoate, ethyl isobutyrate, propylisobutyrate, isopropyl isobutyrate, isobutyl isobutyrate, propylpivalate, isopropyl pivalate, butyl pivalate, and isobutyl pivalate.

Examples of a non-aqueous dispersion medium include the aromaticcompound solvent and the aliphatic compound solvent described above.

It is preferable that the dispersion medium used for the solidelectrolyte composition according to the embodiment of the presentinvention includes a hydrocarbon compound. The hydrocarbon compound is acompound formed of hydrocarbon among the aromatic compound and thealiphatic compound described above. A proportion of the hydrocarboncompound in the dispersion medium is preferably 50 mass % or higher,more preferably 60 mass % or higher, still more preferably 70 mass % orhigher, still more preferably 80 mass % or higher, and still morepreferably 90 mass % or higher. It is also preferable that thedispersion medium is formed of the hydrocarbon compound.

The number of dispersion media in the solid electrolyte composition maybe one or two or more. In a case where the dispersion medium is formedof two or more compounds (solvents), it is preferable that the compoundsare compatible with each other without being phase-separated.

The number of carbon atoms in the compound forming the dispersion mediumis not particularly limited and is preferably 2 to 30, more preferably 4to 20, still more preferably 6 to 15, and still more preferably 7 to 12.

The C Log P value of the compound forming the dispersion medium ispreferably 1 or higher, more preferably 2 or higher, and still morepreferably 3 or higher. The upper limit is not particularly limited andis practically 10 or lower.

In the present invention, the C log P value refers to a value obtainedby calculating a common logarithm Log P of a partition coefficient Pbetween 1-octanol and water. As a method or software used forcalculating the C Log P value, a well-known one can be used. Unlessspecified otherwise, the C Log P value is a value calculated afterdrawing a structure using ChemDraw (manufactured by PerkinElmer Co.,Ltd.).

For example, the C Log P values of the dispersion media described aboveare as follows: toluene (C Log P=2.5), hexane (C Log P=3.9), heptane (CLog P=4.4), octane (C Log P=4.9), cyclohexane (C Log P=3.4), cyclooctane(C Log P=4.5), decalin (C Log P=4.8), dibutyl ketone (C Log P=3.0),dibutyl ether (C Log P=3.0), butyl butyrate (C Log P=2.8), andtributylamine (C Log P=4.8).

The content of the dispersion medium in the solid electrolytecomposition is not particularly limited, but is preferably 20% to 80mass %, more preferably 30% to 70 mass %, and particularly preferably40% to 60 mass %.

<Dispersant>

It is also preferable that the solid electrolyte composition accordingto the embodiment of the present invention includes a dispersant. In acase where the content of any one of the conductive auxiliary agent, theelectrode active material, or the inorganic solid electrolyte is highand/or in a case where the particle size of the electrode activematerial and the inorganic solid electrolyte is small such that thesurface area increases, by adding the dispersant, the aggregationthereof can be further suppressed, and the active material layer can bemore uniformly formed. As the dispersant, a dispersant that is generallyused for an all-solid state secondary battery can be appropriatelyselected and used. Generally, a compound intended for particleadsorption and steric repulsion and/or electrostatic repulsion ispreferably used.

<Other Additives>

As components other than the respective components described above, thesolid electrolyte composition according to the embodiment of the presentinvention may optionally include a lithium salt, an ionic liquid, athickener, a crosslinking agent (an agent causing a crosslinkingreaction by radical polymerization, condensation polymerization, orring-opening polymerization), a polymerization initiator (an agent thatgenerates an acid or a radical by heat or light), an antifoaming agent,a leveling agent, a dehydrating agent, or an antioxidant.

[Method of Manufacturing Solid Electrolyte Composition]

The solid electrolyte composition according to the embodiment of thepresent invention can be prepared by mixing the first binder (B1), thesecond binder (B2), and the inorganic solid electrolyte and optionallythe active material, the conductive auxiliary agent, the additives, andthe like in the presence of the dispersion medium (C) (by dispersing thecomponents the dispersion medium). In the solid electrolyte compositionaccording to the embodiment of the present invention, the second binder(B2) may be dissolved in the dispersion medium. The solid electrolytecomposition according to the embodiment of the present invention ispreferably prepared as a slurry.

The slurry of the solid electrolyte composition can be prepared bymixing the respective components described above using a variety ofmixers (dispersers). The mixer is not particularly limited, and examplesthereof include a ball mill, a beads mill, a planetary mixer, a blademixer, a roll mill, a kneader, a thin-film spin system high-speed mixer,a high-speed rotary stirrer, and a disc mill. The mixing (dispersing)conditions are not particularly limited. However, in a case where a ballmill is used, the inorganic solid electrolyte and the dispersion mediumare preferably mixed together at 150 to 700 rpm (rotation per minute)for 1 to 24 hours. Two dispersers may be used in two or more steps.

In the present invention, the mixing order of the respective componentsis not particularly limited, and the components may be mixed at once orsequentially.

The conductive auxiliary agent and the binder may be mixed in the formof particles without any change but are preferably mixed in the form ofa dispersion liquid in which the conductive auxiliary agent is dispersedin the dispersion medium in advance (a part of the binder may bedissolved in the dispersion medium). As a result, secondary aggregationof the conductive auxiliary agent can be prevented, and the particlesize can be controlled.

The solid electrolyte composition according to the embodiment of thepresent invention is preferably used as a material for forming a solidelectrolyte-containing sheet and a material for forming a solidelectrolyte layer or an electrode active material layer of an all-solidstate secondary battery, the solid electrolyte-containing sheet beingpreferably used for an all-solid state secondary battery.

[Solid Electrolyte-Containing Sheet]

A solid electrolyte-containing sheet according to the embodiment of thepresent invention is a sheet-shaped molded body and includes theinorganic solid electrolyte (A), the binder (B), and a solvent (C1) andoptionally the active material (D), the conductive auxiliary agent (E),and various additives. The inorganic solid electrolyte (A), the binder(B), the active material (D), the conductive auxiliary agent (E), theadditives, and the like have the same definitions as described aboveregarding the solid electrolyte composition according to the embodimentof the present invention.

In addition, the solvent (C1) has the same definition as that of thedispersion medium (C) in the solid electrolyte composition according tothe embodiment of the present invention. That is, the binder (B) in thesolid electrolyte-containing sheet according to the embodiment of thepresent invention includes a binder (first binder (B1)) thatprecipitates after a centrifugal separation process and a binder (secondbinder (B2)) that remains in a supernatant without precipitating afterthe centrifugal separation process at a specific ratio described below,the centrifugal separation process (hereinafter, simply referred to as“ultracentrifugal separation process”) being performed at a temperatureof 25° C. at a centrifugal force of 610000 G for 1 hour in a state wherethe binder (B) is dispersed in the solvent (C1) forming the solidelectrolyte-containing sheet (a part thereof may be dissolved). Afterthe ultracentrifugal separation process, the content of the binder inthe solvent (C1) is 0.1 to 10 mass %.

In the solid electrolyte-containing sheet according to the embodiment ofthe present invention, a relationship between the content X of the firstbinder (B1) and the content Y of the second binder (B2) satisfies thefollowing expression by mass.0.10≤Y/(X+Y)≤0.80

It is preferable that the relationship satisfies the followingexpression.0.10≤Y/(X+Y)≤0.60

It is more preferable that the relationship satisfies the followingexpression.0.10≤Y/(X+Y)≤0.50

It is still more preferable that the relationship satisfies thefollowing expression.0.15≤Y/(X+Y)≤0.45

It is still more preferable that the relationship satisfies thefollowing expression.0.20≤Y/(X+Y)≤0.40

It is preferable that the solid electrolyte-containing sheet accordingto the embodiment of the present invention is formed using the solidelectrolyte composition according to the embodiment of the presentinvention. In this case, the solvent (C1) forming the solidelectrolyte-containing sheet is a residual solvent of the dispersionmedium (C) forming the solid electrolyte composition that remainswithout being volatilized during the formation of the solidelectrolyte-containing sheet.

In the solid electrolyte-containing sheet according to the embodiment ofthe present invention, a preferable range of a content ratio between therespective components forming the solid content is the same as apreferable content ratio between the respective components forming thesolid content in the solid electrolyte composition according to theembodiment of the present invention. In addition, in the solidelectrolyte-containing sheet according to the embodiment of the presentinvention, the content of the solvent (C1) is preferably 0.01% to 10mass % and more preferably 0.1% to 5 mass %.

In the solid electrolyte-containing sheet according to the embodiment ofthe present invention, binding properties between the solid particlesare excellent, and an interface resistance between the solid particlescan be sufficiently suppressed. Therefore, even in a case where anall-solid state secondary battery that is obtained by using the solidelectrolyte-containing sheet according to the embodiment of the presentinvention as a solid electrolyte layer or an electrode active materiallayer in the all-solid state secondary battery is bent with a smallerbend radius, the occurrence of a defect (chipping, cracking, fracturingor peeling) in the layer is suppressed, and excellent batteryperformance can be maintained.

The solid electrolyte-containing sheet according to the embodiment ofthe present invention is preferably obtained by pressure forming.

The solid electrolyte-containing sheet according to the embodiment ofthe present invention can be suitably used as a solid electrolyte layeror an electrode active material layer of an all-solid state secondarybattery.

The solid electrolyte-containing sheet according to the embodiment ofthe present invention may include other members such as a substrate or arelease sheet. In addition, in a case where the solidelectrolyte-containing sheet according to the embodiment of the presentinvention includes the active material, the solid electrolyte-containingsheet can be formed on a metal foil. In this case, in the all-solidstate secondary battery that is formed using the solidelectrolyte-containing sheet, the metal foil can function as a currentcollector. That is, an electrode sheet for an all-solid state secondarybattery can be formed using the metal foil and the solidelectrolyte-containing sheet formed on the metal foil.

Further, in the above-described electrode sheet for an all-solid statesecondary battery, the solid electrolyte-containing sheet according tothe embodiment of the present invention not including the activematerial may be provided on the solid electrolyte-containing sheetincluding the active material. This way, a laminate having a three-layerstructure in which the metal foil, the solid electrolyte-containingsheet including the active material, and the solidelectrolyte-containing sheet not including the active material arelaminated may also be used as the electrode sheet for an all-solid statesecondary battery.

Further, the above-described electrode sheet for an all-solid statesecondary battery may also have a configuration in which the solidelectrolyte-containing sheet including the active material is formed onthe solid electrolyte-containing sheet not including the active materialin the laminate having the above-described three-layer structure. Inthis case, among two solid electrolyte-containing sheets between whichthe solid electrolyte-containing sheet not including the active materialis sandwiched, one solid electrolyte-containing sheet includes apositive electrode active material and another solidelectrolyte-containing sheet includes a negative electrode activematerial.

In the electrode sheet for an all-solid state secondary battery havingthe three- or four-layer structure, at least one of the solidelectrolyte-containing sheet including the active material or the solidelectrolyte-containing sheet not including the active material may bedifferent from the solid electrolyte-containing sheet according to theembodiment of the present invention.

In addition, the electrode sheet for an all-solid state secondarybattery may include other layers such as a substrate (other than acurrent collector), a protective layer (release sheet), a currentcollector, or a coating layer.

The thickness of each of the layers forming the electrode sheet is thesame as the thickness of each of the layers described below regardingthe all-solid state secondary battery according to the embodiment of thepresent invention.

[Method of Manufacturing Solid Electrolyte-Containing Sheet]

A method of manufacturing a solid electrolyte-containing sheet accordingto the embodiment of the present invention is not particularly limited.Examples of the method of manufacturing a solid electrolyte-containingsheet include a method including forming a film (applying and drying) ofthe solid electrolyte composition according to the embodiment of thepresent invention to the substrate or the current collector (otherlayers may be interposed therebetween) to form the active material layer(applied and dried layer) on the substrate or the current collector. Asa result, the solid electrolyte-containing sheet including the substrateor the current collector and the applied and dried layer can beprepared. Here, the applied and dried layer refers to a layer formed byapplying the solid electrolyte composition according to the embodimentof the present invention and drying the dispersion medium (that is, alayer formed using the solid electrolyte composition according to theembodiment of the present invention and made of a composition obtainedby volatilizing the dispersion medium from the solid electrolytecomposition according to the embodiment of the present invention). Inthis case, instead of removing the entire amount of the dispersionmedium, the applied and dried layer may include a residual solvent.

Each of steps of application, drying, or the like in the method ofmanufacturing a solid electrolyte-containing sheet according to theembodiment of the present invention will be described below regarding amethod of manufacturing an all-solid state secondary battery.

In the method of manufacturing a solid electrolyte-containing sheetaccording to the embodiment of the present invention, it is alsopossible to pressurize the applied and dried layer obtained as describedabove. Pressurization conditions or the like will be described belowregarding the method of manufacturing an all-solid state secondarybattery.

In addition, the method of manufacturing a solid electrolyte-containingsheet according to the embodiment of the present invention may include astep of peeling the substrate, the protective layer (particularly, therelease sheet), or the like.

[All-Solid State Secondary Battery]

The all-solid state secondary battery according to the embodiment of thepresent invention includes a positive electrode active material layerand a negative electrode active material layer that is disposed to facethe positive electrode active material layer with the solid electrolytelayer sandwiched therebetween. At least one of the positive electrodeactive material layer, the solid electrolyte layer, or the negativeelectrode active material layer is formed of the solidelectrolyte-containing sheet according to the embodiment of the presentinvention. That is, the all-solid state secondary battery according tothe embodiment of the present invention has any one of a configurationin which one of the positive electrode active material layer, the solidelectrolyte layer, or the negative electrode active material layer isformed of the solid electrolyte-containing sheet according to theembodiment of the present invention, a configuration in which two of thepositive electrode active material layer, the solid electrolyte layer,and the negative electrode active material layer are formed of the solidelectrolyte-containing sheet according to the embodiment of the presentinvention, or a configuration in which three of the positive electrodeactive material layer, the solid electrolyte layer, and the negativeelectrode active material layer are formed of the solidelectrolyte-containing sheet according to the embodiment of the presentinvention.

The thickness of each of the negative electrode active material layer,the solid electrolyte layer, and the positive electrode active materiallayer is not particularly limited. In consideration of the dimension ofa general all-solid state secondary battery, each of the thicknesses ofthe respective layers is preferably 10 to 1,000 μm and more preferably20 μm or more and less than 500 μm. In the all-solid state secondarybattery according to the embodiment of the present invention, thethickness of at least one layer of the positive electrode activematerial layer or the negative electrode active material layer is stillmore preferably 50 μm or more and less than 500 μm.

In the all-solid state secondary battery according to the embodiment ofthe present invention, typically, a current collector is provided on asurface opposite to a surface of each of the positive electrode activematerial layer and the negative electrode active material layer that isin contact with the solid electrolyte layer.

(Case)

Depending on uses, the all-solid state secondary battery according tothe embodiment of the present invention may be used as the all-solidstate secondary battery having the above-described structure as it isbut is preferably sealed in an appropriate case to be used in the formof a dry cell. The case may be a metallic case or a resin (plastic)case. In a case where a metallic case is used, examples thereof includea material for forming an aluminum alloy case, a stainless steel case,or the like. It is preferable that the metallic case is classified intoa positive electrode-side case and a negative electrode-side case andthat the positive electrode-side case and the negative electrode-sidecase are electrically connected to the positive electrode currentcollector and the negative electrode current collector, respectively.The positive electrode-side case and the negative electrode-side caseare preferably integrated by being joined together through a gasket forshort circuit prevention.

Hereinafter, an all-solid state secondary battery according to apreferred embodiment of the present invention will be described withreference to FIG. 1 , but the present invention is not limited thereto.

FIG. 1 is a cross-sectional view schematically illustrating theall-solid state secondary battery (lithium ion secondary battery)according to the preferred embodiment of the present invention. In thecase of being seen from the negative electrode side, an all-solid statesecondary battery 10 of the present embodiment includes a negativeelectrode current collector 1, a negative electrode active materiallayer 2, a solid electrolyte layer 3, a positive electrode activematerial layer 4, and a positive electrode current collector 5 in thisorder. The respective layers are in contact with one another and have alaminated structure. In a case in which the above-described structure isemployed, during charging, electrons (e) are supplied to the negativeelectrode side, and lithium ions (Li⁺) are accumulated in the negativeelectrode side. On the other hand, during discharging, the lithium ions(Li⁺) accumulated in the negative electrode side return to the positiveelectrode, and electrons are supplied to an operation portion 6. In anexample illustrated in the drawing, an electric bulb is employed as theoperation portion 6 and is lit by discharging.

The solid electrolyte composition according to the embodiment of thepresent invention can be preferably used as a material for forming theactive material layer, in particular, as a material for forming thenegative electrode active material layer. In addition, the solidelectrolyte-containing sheet according to the embodiment of the presentinvention is suitable as the negative electrode active material layerand the positive electrode active material layer.

In the present specification, the positive electrode active materiallayer and the negative electrode active material layer will becollectively referred to as the active material layer.

In a case where the all-solid state secondary battery having a layerconfiguration illustrated in FIG. 1 is put into, for example, a2032-type coin case, the all-solid state secondary battery will bereferred to as “electrode sheet for an all-solid state secondarybattery”, and a battery prepared by putting this electrode sheet for anall-solid state secondary battery into a 2032-type coin case will bereferred to as “all-solid state secondary battery”, thereby referring toboth batteries distinctively in some cases.

(Positive Electrode Active Material Layer, Solid Electrolyte Layer, andNegative Electrode Active Material Layer)

In the all-solid state secondary battery 10, at least one of thepositive electrode active material layer 4, the solid electrolyte layer3, or the negative electrode active material layer 2 is formed using thesolid electrolyte composition according to the embodiment of the presentinvention or the solid electrolyte-containing sheet according to theembodiment of the present invention.

The respective components included in the positive electrode activematerial layer 4, the solid electrolyte layer 3, and the negativeelectrode active material layer 2 may be the same as or different fromeach other.

In the all-solid state secondary battery 10, the negative electrodeactive material layer can be formed as a lithium metal layer. Examplesof the lithium metal layer include a layer formed by deposition orforming of lithium metal powder, a lithium foil, and a lithium depositedfilm. The thickness of the lithium metal layer is not limited to theabove-described thickness of the above-described negative electrodeactive material layer and may be, for example, 1 to 500 μm.

The positive electrode current collector 5 and the negative electrodecurrent collector 1 are preferably an electron conductor.

In the present invention, either or both of the positive electrodecurrent collector and the negative electrode current collector will alsobe simply referred to as the current collector.

As a material for forming the positive electrode current collector, notonly aluminum, an aluminum alloy, stainless steel, nickel, or titaniumbut also a material (a material on which a thin film is formed) obtainedby treating the surface of aluminum or stainless steel with carbon,nickel, titanium, or silver is preferable. Among these, aluminum or analuminum alloy is more preferable.

As a material for forming the negative electrode current collector, notonly aluminum, copper, a copper alloy, stainless steel, nickel, ortitanium but also a material obtained by treating the surface ofaluminum, copper, a copper alloy, or stainless steel with carbon,nickel, titanium, or silver is preferable, and aluminum, copper, acopper alloy, or stainless steel is more preferable.

Regarding the shape of the current collector, typically, currentcollectors having a film sheet-like shape are used, but it is alsopossible to use net-shaped collectors, punched collectors, compacts oflath bodies, porous bodies, foaming bodies, or fiber groups, and thelike.

The thickness of the current collector is not particularly limited, butis preferably 1 to 500 μm. In addition, it is also preferable that thesurface of the current collector is made to be uneven through a surfacetreatment.

In the present invention, a functional layer, a member, or the like maybe appropriately interposed or disposed between the respective layers ofthe negative electrode current collector, the negative electrode activematerial layer, the solid electrolyte layer, the positive electrodeactive material layer, and the positive electrode current collector oron the outside thereof. In addition, each of the layers may have asingle-layer structure or a multi-layer structure.

[Method of Manufacturing All-Solid State Secondary Battery]

The all-solid state secondary battery can be manufactured using atypical method, except that at least one of the positive electrodeactive material layer, the solid electrolyte layer, or the negativeelectrode active material layer is formed using the solid electrolytecomposition according to the embodiment of the present invention or thesolid electrolyte-containing sheet according to the embodiment of thepresent invention. An example of manufacturing the all-solid statesecondary battery according to the embodiment of the present inventionwill be described below.

The all-solid state secondary battery according to the embodiment of thepresent invention can be manufactured using a method including: a stepof applying the solid electrolyte composition according to theembodiment of the present invention to a substrate (for example, a metalfoil as a current collector) to form a coating film thereon; and a stepof drying the coating film. That is, the all-solid state secondarybattery according to the embodiment of the present invention can bemanufactured through the above-described method of manufacturing a solidelectrolyte-containing sheet according to the embodiment of the presentinvention.

For example, the solid electrolyte composition including the positiveelectrode active material is applied as a positive electrode compositionto a metal foil which is a positive electrode current collector and isdried so as to form a positive electrode active material layer. As aresult, a positive electrode sheet for an all-solid state secondarybattery is prepared. Next, the solid electrolyte layer-formingcomposition for forming a solid electrolyte layer is applied to thepositive electrode active material layer and is dried so as to form thesolid electrolyte layer. Furthermore, the solid electrolyte compositionincluding the negative electrode active material is applied as thenegative electrode composition to the solid electrolyte layer and isdried so as to form a negative electrode active material layer. Bylaminating the negative electrode current collector (metal foil) on thenegative electrode active material layer, an all-solid state secondarybattery having a structure in which the solid electrolyte layer issandwiched between the positive electrode active material layer and thenegative electrode active material layer can be obtained. Theabove-described drying is not necessarily performed for each layer, andthe composition may be dried after being applied in multiple layers.Optionally by sealing the laminate in a case, a desired all-solid statesecondary battery can be obtained.

In addition, an all-solid state secondary battery can also bemanufactured by forming the negative electrode active material layer,the solid electrolyte layer, and the positive electrode active materiallayer on the negative electrode current collector in order reverse tothat of the method of forming the respective layers and laminating thepositive electrode current collector thereon.

As another method, for example, the following method can be used. Thatis, the positive electrode sheet for an all-solid state secondarybattery is prepared as described above. In addition, the solidelectrolyte composition including the negative electrode active materialis applied as a negative electrode composition to a metal foil which isa negative electrode current collector so as to form a negativeelectrode active material layer. As a result, a negative electrode sheetfor an all-solid state secondary battery is prepared. Next, the solidelectrolyte layer is formed on the active material layer in any one ofthe sheets as described above. Furthermore, the other one of thepositive electrode sheet for an all-solid state secondary battery andthe negative electrode sheet for an all-solid state secondary battery islaminated on the solid electrolyte layer such that the solid electrolytelayer and the active material layer come into contact with each other.This way, an all-solid state secondary battery can be manufactured.

As still another method, for example, the following method can be used.That is, the positive electrode sheet for an all-solid state secondarybattery and the negative electrode sheet for an all-solid statesecondary battery are produced as described above. In addition,separately from the electrode sheets, the solid electrolytelayer-forming composition is applied to a substrate to prepare a solidelectrolyte-containing sheet for an all-solid state secondary batteryincluding the solid electrolyte layer. Furthermore, the positiveelectrode sheet for an all-solid state secondary battery and thenegative electrode sheet for an all-solid state secondary battery arelaminated such that the solid electrolyte layer removed from thesubstrate is sandwiched therebetween. This way, an all-solid statesecondary battery can be manufactured.

An all-solid state secondary battery can also be manufactured bycombining the above-described forming methods. For example, the positiveelectrode sheet for an all-solid state secondary battery, the negativeelectrode sheet for an all-solid state secondary battery, and the solidelectrolyte-containing sheet for an all-solid state secondary batteryare prepared respectively. Next, the solid electrolyte layer removedfrom the substrate is laminated on the negative electrode sheet for anall-solid state secondary battery, and the positive electrode sheet foran all-solid state secondary battery is bonded thereto. As a result, anall-solid state secondary battery can be manufactured. In this method,it is also possible to laminate the solid electrolyte layer on thepositive electrode sheet for an all-solid state secondary battery and tobond the solid electrolyte layer to the negative electrode sheet for anall-solid state secondary battery.

<Formation of Respective Layers (Film Formation)>

A method of applying the solid electrolyte composition to form the layerof the all-solid state secondary battery is not particularly limited andcan be appropriately selected. Examples of the method include coating(preferably wet-type coating), spray coating, spin coating, dip coating,slit coating, stripe coating, and bar coating.

In this case, the solid electrolyte composition or the like may be driedafter being applied each time or may be dried after being applied inmultiple layers. The drying temperature is not particularly limited andis preferably 30° C. or higher, more preferably 60° C. or higher, andstill more preferably 80° C. or higher. In addition, the dryingtemperature is preferably 300° C. or lower, more preferably 250° C. orlower, and still more preferably 200° C. or lower. In a case where thesolid electrolyte composition is heated in the above-describedtemperature range, the dispersion medium can be sufficiently volatilizedto make the composition enter a solid state (applied and dried layer).In addition, the temperature is not excessively increased, and therespective members of the all-solid state secondary battery are notimpaired, which is preferable.

It is preferable that each of the layers formed during the preparationof the all-solid state secondary battery is pressurized after theformation. In addition, the respective layers are also preferablypressurized in a state where they are laminated. Examples of thepressurization method include a method using a hydraulic cylinderpressing machine. A pressure is not particularly limited and may be apressure at which the particle shape of the above-described components,for example, the inorganic solid electrolyte is lost. As describedabove, the above-described contact state and binding state of the solidparticles can be realized by forming a film using the solid electrolytecomposition according to the embodiment of the present invention and donot significantly deteriorate even after a pressure is applied thereto.For example, the pressure is preferably in a range of 50 to 1500 MPa.

In addition, the applied solid electrolyte composition may be heatedwhile being pressurized. The heating temperature is not particularlylimited, but is generally in a range of 30° C. to 300° C. The respectivelayers or the all-solid state secondary battery can also be pressed at atemperature higher than the glass transition temperature of theinorganic solid electrolyte.

The atmosphere during the pressurization is not particularly limited andmay be any one of in the atmosphere, under the dried air (the dew point:−20° C. or lower), in an inert gas (for example, in an argon gas, in ahelium gas, or in a nitrogen gas), and the like.

The pressing time may be a short time (for example, within severalhours) at a high pressure or a long time (one day or longer) under theapplication of an intermediate pressure. In addition, a restrainingdevice (screw fastening pressure or the like) of the all-solid statesecondary battery can also be used in order to continuously apply anintermediate pressure.

The pressing pressure may be homogeneous or variable with respect to apressed portion such as a sheet surface.

The pressing pressure may be variable depending on the area or thethickness of the pressed portion. In addition, the pressure may also bevariable stepwise for the same portion.

A pressing surface may be smooth or roughened.

<Initialization>

The all-solid state secondary battery manufactured as described above ispreferably initialized after the manufacturing or before the use. Theinitialization is not particularly limited, and it is possible toinitialize the all-solid state secondary battery by, for example,carrying out initial charging and discharging in a state in which thepressing pressure is increased and then releasing the pressure up to apressure at which the all-solid state secondary battery is ordinarilyused.

[Usages of All-Solid State Secondary Battery]

The all-solid state secondary battery according to the embodiment of thepresent invention can be applied to a variety of usages. Applicationaspects are not particularly limited, and, in the case of being mountedin electronic devices, examples thereof include notebook computers,pen-based input personal computers, mobile personal computers, e-bookplayers, mobile phones, cordless phone handsets, pagers, handyterminals, portable faxes, mobile copiers, portable printers, headphonestereos, video movies, liquid crystal televisions, handy cleaners,portable CDs, mini discs, electric shavers, transceivers, electronicnotebooks, calculators, portable tape recorders, radios, backup powersupplies, and memory cards. Additionally, examples of consumer usagesinclude automobiles (electric cars and the like), electric vehicles,motors, lighting equipment, toys, game devices, road conditioners,watches, strobes, cameras, medical devices (pacemakers, hearing aids,and shoulder massage devices, and the like). Furthermore, the all-solidstate secondary battery can be used for a variety of military usages anduniverse usages. In addition, the all-solid state secondary battery canalso be combined with solar batteries.

EXAMPLES

The present invention will be described in more detail based on Examplesbut is not limited to these examples.

[Synthesis of Sulfide-Based Inorganic Solid Electrolyte Li—P—S-BasedGlass]

As a sulfide-based inorganic solid electrolyte, Li—P—S-based glass wassynthesized with reference to a non-patent document of T. Ohtomo, A.Hayashi, M. Tatsumisago, Y. Tsuchida, S. HamGa, K. Kawamoto, Journal ofPower Sources, 233, (2013), pp. 231 to 235 and A. Hayashi, S. Hama, H.Morimoto, M. Tatsumisago, T. Minami, Chem. Lett., (2001), pp. 872 and873.

Specifically, in a glove box under an argon atmosphere (dew point: −70°C.), lithium sulfide (Li₂S, manufactured by Aldrich-Sigma, Co. LLC.Purity: >99.98%) (2.42 g) and diphosphoruspentasulfide (P₂S₅,manufactured by Aldrich-Sigma, Co. LLC. Purity: >99%) (3.90 g) wererespectively weighed, put into an agate mortar, and mixed using an agatemuddler for five minutes. The mixing ratio between Li₂S and P₂S₅(Li₂S:P₂S₅) was set to 75:25 in terms of molar ratio.

66 g of zirconia beads having a diameter of 5 mm were put into a 45 mLzirconia container (manufactured by Fritsch Japan Co., Ltd.), the fullamount of the mixture of the lithium sulfide and thediphosphoruspentasulfide was put thereinto, and the container wascompletely sealed in an argon atmosphere. The container was set in aplanetary ball mill P-7 (trade name; manufactured by Fritsch Japan Co.,Ltd.), mechanical milling was carried out at a temperature of 25° C. anda rotation speed of 510 rpm for 20 hours. As a result, 6.20 g of ayellow powder of a sulfide-based inorganic solid electrolyte(Li—P—S-based glass; hereinafter, referred to as Li—P—S) was obtained.

[Preparation of Binder Solution]

<Preparation of Binder E-1 Solution>

53.7 g of toluene was put into a 300 mL three-neck flask and was heatedto 80° C. under stirring (solution A). Separately, 15.0 g of methylmethacrylate, 38.2 g of dodecyl methacrylate, 0.54 g of3-mercaptoisobutyric acid, and 0.53 g of V-601 (trade name, manufacturedby Wako Pure Chemical Industries, Ltd.) were added to a 100 mL measuringcylinder and were stirred to be uniformly dissolved (solution B). Thesolution B was added dropwise to the solution A at 80° C. for 2 hours.Next, the solution was further stirred at 80° C. for 2 hours, wasstirred at 95° C. for 2 hours, and was cooled to room temperature. Anoperation of putting this polymer solution into methanol, precipitatingthe polymer, and removing the solvent was repeated twice. Next, 107 g ofheptane was added to the precipitate to prepare a heptane solution. Thisheptane solution was set as a binder E-1 solution. The solid contentconcentration in the binder E-1 solution was 43 mass %. In the binderE-1 solution, the weight-average molecular weight (Mw) of the polymerwas 10000, and the number-average molecular weight (Mn) of the polymerwas 5000.

<Preparation of Binder E-2 Solution>

A binder E-2 solution was obtained using the same preparation method asthat of the binder E-1 solution, except that the amount of V-601 (tradename, manufactured by Wako Pure Chemical Industries, Ltd.) was changedto 0.20 g. The solid content concentration in the binder E-2 solutionwas 40 mass %. In addition, in the binder E-2 solution, Mw of thepolymer was 50000, and Mn of the polymer was 20000.

<Preparation of Binder Solution E-3>

A binder E-3 solution was obtained using the same preparation method asthat of the binder E-1 solution, except that dodecyl methacrylate waschanged to 2-hydroxyethyl acrylate. The solid content concentration inthe binder E-3 solution was 41 mass %. In addition, in the binder E-3solution, Mw of the polymer was 12000, and Mn of the polymer was 7000.

<Preparation of Binder Solution E-4>

A binder E-4 solution was obtained using the same preparation method asthat of the binder E-1 solution, except that dodecyl methacrylate waschanged to ethyl acrylate. The solid content concentration in the binderE-4 solution was 43 mass %. In addition, in the binder E-4 solution, Mwof the polymer was 12000, and Mn of the polymer was 6000.

[Preparation of Binder Mixed Solution]

<Preparation of Binder B-1 Mixed Solution>

11.5 g of the binder E-1 solution and 18.5 g of heptane were put into a200 mL three-neck flask and were heated to 80° C. under stirring(solution A). Separately, 10.0 g of 2-hydroxyethyl acrylate, 1.68 g ofmono(2-acryloyloxyethyl) succinate, and 0.53 g of V-601 (trade name,manufactured by Wako Pure Chemical Industries, Ltd.) were added to a 50mL measuring cylinder and were stirred to be uniformly dissolved(solution B). The solution B was added dropwise to the solution A at 80°C. for 2 hours. Next, the solution was further stirred at 80° C. for 2hours, was stirred at 90° C. for 2 hours, was polymerized, and wascooled to room temperature. This way, a part of the binder was dispersedin the heptane to obtain a dispersion liquid. This dispersion liquid wasset as a binder B-1 mixed solution. The volume average particle size ofa particulate binder forming a dispersoid of the binder B-1 mixedsolution was 190 nm.

In the binder B-1 mixed solution, polymers having variouscharacteristics or properties are present in a state where variousstates are mixed. For example, in the binder B-1 mixed solution, thebinder E-1 was present in a state where it was dissolved in thedispersion medium (heptane), or was present by adsorption or the like inor on a three-dimensional structure of the polymerization reactantduring the preparation of the binder B-1 mixed solution. In addition, inthe binder B-1 mixed solution, a large amount of the polymerizationreactant during the preparation of the binder B-1 mixed solution waspresent in the form of particles (dispersed state). However, apolymerization reactant having a low molecular weight was present in astate where it was dissolved in the dispersion medium, or as fineparticles having a small particle size.

That is, the polymer present in the binder B-1 mixed solution wasdissolved, was present in the form of particles having various sizes,and was adsorbed to the inside or the surfaces of the particles althoughit was soluble. In addition, the polymer present in the binder B-1 mixedsolution also has a wide molecular weight distribution.

The same is applicable to binder B-2 to B-4 mixed solutions describedbelow.

<Preparation of Binder B-2 Mixed Solution>

A binder B-2 mixed solution was obtained using the same preparationmethod as that of the binder B-1 mixed solution, except that the binderE-2 solution was used instead of the binder E-1 solution. The volumeaverage particle size of a particulate binder forming a dispersoid ofthe binder B-2 mixed solution was 150 nm.

<Preparation of Binder B-3 Mixed Solution>

A binder B-3 mixed solution was obtained using the same preparationmethod as that of the binder B-1 mixed solution, except that the binderE-3 solution was used instead of the binder E-1 solution. The volumeaverage particle size of a particulate binder forming a dispersoid ofthe binder B-3 mixed solution was 220 nm.

<Preparation of Binder B-4 Mixed Solution>

A binder B-4 mixed solution was obtained using the same preparationmethod as that of the binder B-1 mixed solution, except that the binderE-4 solution was used instead of the binder E-1 solution. The volumeaverage particle size of a particulate binder forming a dispersoid ofthe binder B-4 mixed solution was 200 nm.

[Ultracentrifugal Separation Process of Binder Mixed Solution]

Each of the binder B-1 to B-4 mixed solutions prepared as describedabove was diluted with heptane to obtain diluted mixed solutionincluding 0.8 mass % of the polymer in total. 16 g of the diluted mixedsolution (including 0.128 g of the polymer) was put into a polypropylenetube (manufactured by Hitachi Koki Co., Ltd.) and was sealed with a tubesealer (manufactured by Hitachi Koki Co., Ltd.). Next, this tube was setin a loader of a micro-ultracentrifuge (trade name: himac CS-150 FNX,manufactured by Hitachi Koki Co., Ltd.) and was processed with anultracentrifugal separation process under conditions of 100000 rpm and25° C. for 1 hour. The centrifugal force of the ultracentrifugalseparation process was 610000 G (the centrifugal force was applied tothe bottom of the tube). Due to this process, a precipitated binder anda binder that remained in a supernatant without precipitating wereseparated.

[Preparation of Binder (B)-Containing Solution]

<Preparation of Binder S-1-Containing Solution>

A precipitated binder a1 (first binder (B1)) and a binder a2 (secondbinder (B2)) that remained in a supernatant were mixed with heptane toobtain a binder S-1-containing solution, the binders being obtained byprocessing the binder B-1 mixed solution in [Ultracentrifugal SeparationProcess of Binder Mixed Solution]. Specifically, the three componentswere put into a vial tube such that the amount of the binder a1 was0.11264 g, the amount of the binder a2 was 0.01536 g, and the amount ofheptane was 1.152 g, and were stirred using a mix rotor for 30 minutes.As a result, the binder S-1-containing solution was prepared. In thebinder S-1-containing solution, the first binder (B1) was in the form ofparticles having a particle size of about 100 to 300 nm.

<Preparation of Binder S-2-Containing Solution>

A binder S-2-containing solution was prepared using the same preparationmethod as that of the binder S-1-containing solution, except that theamount of the binder a1 put into the vial tube was changed to 0.08960 gand the amount of the binder a2 put into the vial tube was 0.03840 g.

<Preparation of Binder S-3-Containing Solution>

A binder S-3-containing solution was prepared using the same preparationmethod as that of the binder S-1-containing solution, except that theamount of the binder a1 put into the vial tube was changed to 0.06400 gand the amount of the binder a2 put into the vial tube was 0.06400 g.

<Preparation of Binder S-4-Containing Solution>

A binder S-4-containing solution was prepared using the same preparationmethod as that of the binder S-1-containing solution, except that theamount of the binder a1 put into the vial tube was changed to 0.03200 gand the amount of the binder a2 put into the vial tube was 0.09600 g.

<Preparation of Binder S-5-Containing Solution>

A precipitated binder b1 (first binder (B1)) and a binder b2 (secondbinder (B2)) that remained in a supernatant were mixed with heptane toobtain a binder S-5-containing solution, the binders being obtained byprocessing the binder B-2 mixed solution in [Ultracentrifugal SeparationProcess of Binder Mixed Solution] Specifically, the three componentswere put into a vial tube such that the amount of the binder b1 was0.10880 g, the amount of the binder b2 was 0.01920 g, and the amount ofheptane was 1.152 g, and were stirred using a mix rotor for 30 minutes.As a result, the binder S-5-containing solution was prepared. In thebinder S-5-containing solution, the first binder (B1) was in the form ofparticles having a particle size of about 150 to 230 nm.

<Preparation of Binder S-6-Containing Solution>

A precipitated binder c1 (first binder (B1)) and a binder c2 (secondbinder (B2)) that remained in a supernatant were mixed with heptane toobtain a binder S-6-containing solution, the binders being obtained byprocessing the binder B-3 mixed solution in [Ultracentrifugal SeparationProcess of Binder Mixed Solution]. Specifically, the three componentswere put into a vial tube such that the amount of the binder c1 was0.08960 g, the amount of the binder c2 was 0.03840 g, and the amount ofheptane was 1.152 g, and were stirred using a mix rotor for 30 minutes.As a result, the binder S-6-containing solution was prepared. In thebinder S-6-containing solution, the first binder (B1) was in the form ofparticles having a particle size of about 110 to 190 nm.

<Preparation of Binder S-7-Containing Solution>

A precipitated binder d1 (first binder (B1)) and a binder d2 (secondbinder (B2)) that remained in a supernatant were mixed with heptane toobtain a binder S-7-containing solution, the binders being obtained byprocessing the binder B-4 mixed solution in [Ultracentrifugal SeparationProcess of Binder Mixed Solution]. Specifically, the three componentswere put into a vial tube such that the amount of the binder d1 was0.08960 g, the amount of the binder d2 was 0.03840 g, and the amount ofheptane was 1.152 g, and were stirred using a mix rotor for 30 minutes.As a result, the binder S-7-containing solution was prepared. In thebinder S-7-containing solution, the first binder (B1) was in the form ofparticles having a particle size of about 320 to 410 nm.

<Preparation of Binder T-1-Containing Solution>

A binder T-1-containing solution was prepared using the same preparationmethod as that of the binder S-1-containing solution, except that theamount of the binder a1 put into the vial tube was changed to 0.11904 gand the amount of the binder a2 put into the vial tube was 0.00896 g.

<Preparation of Binder T-2-Containing Solution>

A binder T-2-containing solution was prepared using the same preparationmethod as that of the binder S-1-containing solution, except that theamount of the binder a1 put into the vial tube was changed to 0.01280 gand the amount of the binder a2 put into the vial tube was 0.11520 g.

<Preparation of Binder T-3-Containing Solution>

The binder B-1 mixed solution prepared as described above was dilutedwith heptane to obtain diluted mixed solution including 0.8 mass % ofthe polymer in total. 16 g of the diluted mixed solution (including0.128 g of the polymer) was put into a polypropylene tube (manufacturedby Hitachi Koki Co., Ltd.) and was sealed with a tube sealer(manufactured by Hitachi Koki Co., Ltd.). Next, this tube was set in aloader of a micro-ultracentrifuge (trade name: himac CS-150 FNX,manufactured by Hitachi Koki Co., Ltd.) and was processed with anultracentrifugal separation process under conditions of 50000 rpm and25° C. for 1 hour. The centrifugal force of the ultracentrifugalseparation process was 305000 G (the centrifugal force was applied tothe bottom of the tube). Due to this process, a precipitated binder a1-2and a binder a2-2 that remained in a supernatant without precipitatingwere separated.

A binder T-3-containing solution was prepared using the same preparationmethod as that of the binder S-1-containing solution, except that thebinder a1-2 was used instead of the binder a1, the amount of the bindera1-2 put into the vial tube was 0.08960 g, the binder a2-2 was usedinstead of the binder a2, and the amount of the binder a2-2 put into thevial tube was 0.03840 g.

The binder compositions of the binder (B)-containing solutions preparedas described above are collectively shown in the following table.

TABLE 1 Binder (B)-Containing Solution First Binder (B1) Second Binder(B2) Kind Kind Amount Kind Amount Tg Y/(X + Y) S-1 a1 0.11264 g a20.01536 g −15 0.12 S-2 a1 0.08960 g a2 0.03840 g −15 0.30 S-3 a1 0.06400g a2 0.06400 g −15 0.50 S-4 a1 0.03200 g a2 0.09600 g −15 0.75 S-5 b10.10880 g b2 0.01920 g −18 0.15 S-6 c1 0.08960 g c2 0.03840 g 5 0.30 S-7d1 0.08960 g d2 0.03840 g 25 0.30 T-1 a1 0.11904 g a2 0.00896 g −15 0.07T-2 a1 0.01280 g a2 0.11520 g −15 0.90 T-3 a1-2 0.08960 g a2-2 0.03840 g−22 0.30

[Preparation Example 1] Preparation of Solid Electrolyte Composition

180 zirconia beads having a diameter of 5 mm were put into a 45 mLzirconia container (manufactured by Fritsch Japan Co., Ltd.), theinorganic solid electrolyte shown in the following table, the binder(B)-containing solution prepared as described above, and heptane as adispersion medium were put thereinto. Next, the container was set in aplanetary ball mill P-7 (trade name, manufactured by Fritsch Japan Co.,Ltd.) and the components were continuously mixed for 2 hours at roomtemperature and a rotation speed of 300 rpm. As a result, a solidelectrolyte composition was prepared.

In a case where the solid electrolyte composition includes a conductiveauxiliary agent, the above-described inorganic solid electrolyte, thebinder (B)-containing solution prepared as described, the conductiveauxiliary agent, and heptane as the dispersion medium were mixed witheach other using the ball mill P-7 to prepare the solid electrolytecomposition.

In a case where the solid electrolyte composition includes an activematerial, the active material was put thereinto, and the components weremixed at room temperature and a rotation speed of 150 rpm for 5 minutes.As a result, a solid electrolyte composition was prepared.

[Preparation Example 2] Preparation of Solid Electrolyte-ContainingSheet

Each of the solid electrolyte compositions prepared as described abovewas applied to a stainless steel (SUS) foil having a thickness of 20 μmas a current collector using a bar coater. The laminate was placed on ahot plate such that the SUS foil faced a lower surface, was heated at80° C. for 1 hour to volatilize and remove the dispersion medium (evenafter the removal, a part of the dispersion medium remained as aresidual solvent), and was pressurized under 300 MPa. As a result, asolid electrolyte-containing sheet was prepared.

Test Example 1] Mandrel Test

Each of the solid electrolyte-containing sheets obtained in PreparationExample 2 was cut in a rectangular shape of 3 cm×14 cm. The cut sheetwas bent using a cylindrical mandrel tester “Product Code 056” (mandreldiameter: 10 mm, manufactured by Allgood Plc.) according to JapaneseIndustrial Standards (JIS) K5600-5-1 (bend resistance (cylindricalmandrel: a test using a test machine type 2); the same test as that ofInternational Standards (ISO) 1519). After bending, a range of 3 cm×8 cmincluding the bent portion was observed by visual inspection, the defectoccurrence of state was evaluated. And the strength of the sheet wasevaluated by evaluating the defect occurrence of state based on thefollowing evaluation standards.

<Mandrel Test Evaluation Standards>

A: A defect (chipping, cracking, fracturing, or peeling) was notobserved

B: the area ratio of the defect portion in the area to be observed washigher than 0% and 10% or lower

C: the area ratio of the defect portion in the area to be observed washigher than 10% and 30% or lower

D: the area ratio of the defect portion in the area to be observed washigher than 30% and 50% or lower

E: the area ratio of the defect portion in the area to be observed washigher than 50%

The results are shown in the table below.

[Test Example 2] Ion Conductivity

After the mandrel test, in each of the solid electrolyte-containingsheets, two circular sheets having a diameter of 14.5 mm were cut from arange where the defect portion was not observed by visual inspection.The solid electrolyte layers (in a case where the active material wasincluded, the electrode layers) of the cut two sheets were bonded toeach other to form a sheet for ion conductivity measurement, and thesheet for ion conductivity measurement was put into a 2032-type coincase 11 formed of stainless steel equipped with a spacer and a washer(not shown in FIG. 2 ). By swaging the 2032-type coin case 11, a testspecimen for ion conductivity measurement having a configuration shownin FIG. 2 fastened with a force of 8 N was prepared.

Using the test specimen for ion conductivity measurement obtained asdescribed above, the ion conductivity was measured. Specifically, thealternating current impedance was measured at a voltage magnitude of 5mV in a frequency range of 1 MHz to 1 Hz using a 1255B frequencyresponse analyzer (trade name, manufactured by SOLARTRON) in aconstant-temperature tank at 30° C. As a result, the resistance of thebonded solid electrolyte-containing sheets (the sheet for ionconductivity measurement) in the thickness direction was obtained, andthe ion conductivity was obtained by calculation from the followingExpression (1). The obtained ion conductivity was evaluated based on thefollowing evaluation standards.ion conductivity σ(mS/cm)=1000×Sample Thickness (cm)/(Resistance(Ω)×Sample Area (cm²))  Expression (1)

In Expression (1), the sample thickness refers to the thickness of thesolid electrolyte layer or the electrode layer.

<Ion Conductivity Evaluation Standards>

AA: 0.65≤σ

A: 0.60≤σ≤0.65

B: 0.50≤σ<0.60

C: 0.40≤σ<0.50

D: 0.30≤σ<0.40

E: 0.20≤σ<0.30

F: σ<0.20

The results are shown in the table below.

The composition shown below in the table are the composition (by mass)of the solid electrolyte composition prepared in Preparation Example 1.

TABLE 2 Inorganic Solid Binder (B)- Conductive Electrolyte ContainingDispersion Medium Active Material Auxiliary Agent (A) Solution (C) (D)(E) No. Kind Amount Kind Amount Kind Amount Kind Amount Kind Amount 11Li—P—S 29 S-1 14 Heptane 57 — 0 — 0 12 Li—P—S 29 S-2 14 Heptane 57 — 0 —0 13 Li—P—S 29 S-3 14 Heptane 57 — 0 — 0 14 Li—P—S 29 S-4 14 Heptane 57— 0 — 0 15 Li—P—S 29 S-5 14 Heptane 57 — 0 — 0 16 Li—P—S 29 S-6 14Heptane 57 — 0 — 0 17 Li—P—S 29 S-7 14 Heptane 57 — 0 — 0 18 Li—P—S 26S-4 39 Heptane 35 — 0 — 0 19 Li—P—S 26 S-2 39 Heptane 35 — 0 — 0 20Li—P—S 14 S-1 5 Heptane 46 NMC 33 AB 2 21 Li—P—S 14 S-2 5 Heptane 46 NMC33 AB 2 22 Li—P—S 14 S-3 5 Heptane 46 NMC 33 AB 2 23 Li—P—S 14 S-4 5Heptane 46 NMC 33 VGCF 2 24 Li—P—S 14 S-5 5 Heptane 46 NCA 33 — 0 25Li—P—S 14 S-6 5 Heptane 46 NCA 33 — 0 26 LLT 14 S-7 5 Heptane 46 NMC 33AB 2 c11 Li—P—S 29 T-1 14 Heptane 57 — 0 — 0 c12 Li—P—S 29 T-2 14Heptane 57 — 0 — 0 c13 Li—P—S 14 T-1 5 Heptane 46 NMC 33 AB 2 c14 Li—P—S14 T-2 5 Heptane 46 NMC 33 AB 2 c15 Li—P—S 14 T-3 5 Heptane 46 NMC 33 AB2 Evaluation Mandrel Result of Ion Sample Test Conductivity ThicknessEvaluation after Mandrel No. Y/(Y + Z) (μm) Result Test Note 11 0.006085 B A Present Invention 12 0.0148 76 A AA Present Invention 13 0.024488 B B Present Invention 14 0.0361 91 C B Present Invention 15 0.0074 88B A Present Invention 16 0.0148 90 C B Present Invention 17 0.0148 88 BB Present Invention 18 0.1011 82 C C Present Invention 19 0.0431 83 A BPresent Invention 20 0.0040 84 A A Present Invention 21 0.0099 87 A AAPresent Invention 22 0.0164 85 A B Present Invention 23 0.0260 85 B APresent Invention 24 0.0050 84 B C Present Invention 25 0.0099 82 B BPresent Invention 26 0.0099 87 B C Present Invention c11 0.0018 85 E EComparative Example c12 0.0225 83 E F Comparative Example c13 0.0012 90E F Comparative Example c14 0.0150 82 E F Comparative Example c15 0.005082 E F Comparative Example “Amount”: Part(s) by Mass

<Notes in Table>

(A): inorganic solid electrolyte

LLT: Li_(0.33)La_(0.55)TiO₃ (average particle size: 3.25 μm,manufactured by Toshima Manufacturing Co., Ltd.)

Li—P—S: Li—P—S-based glass synthesized above

(D): active material

NMC: LiNi_(1/3)CO_(1/3)Mn_(1/3)O₂ (lithium nickel manganese cobaltoxide)

NCA: LiNi_(0.85)Co_(0.10)Al_(0.05)O₂ (lithium nickel cobalt aluminumoxide)

(E): conductive auxiliary agent

AB: acetylene black

VGCF: trade name, carbon fiber, manufactured by Showa Denko K.K.

As shown in Table 2, it was found that, in a case where the componentcomposition of the binder (B) in the solid electrolyte-containing sheetdid not satisfy the range of the present invention, a defect was likelyto occur in the mandrel test and the solid electrolyte-containing sheetwas weak for bending (No. c11 to c15).

In addition, in a case where a portion where a defect was not observedby visual inspection after the mandrel test was selected from the solidelectrolyte-containing sheet and the ion conductivity thereof wasmeasured, the ion conductivity was poor (No. c11 to c15). This showsthat a large number of microscopic defects occurred by bending.

Here, the binder T-3 containing solution was different from the range ofthe present invention in the ultracentrifugal separation condition ofthe binder B-1 mixed solution. The amount of the precipitate componentafter the ultracentrifugal separation of the binder B-1 mixed solutionwas visually the same as the amount of the precipitate component afterthe process of the binder mixed solution B-1 under the ultracentrifugalseparation condition defined by the present invention, and thetransparency of the supernatant component was also the same. However,the evaluation results were poor as shown in Table 2. That is, it wasfound that, in order to exhibit the effects of the present invention, itis important to classify the binder into two binders through thespecific ultracentrifugal separation process defined by the presentinvention and to adjust the amounts of the respective binders at thespecific ratio.

On the other hand, it was found that, in a case where the componentcomposition of the binder (B) that may be included in the solidelectrolyte-containing sheet satisfies the range of the presentinvention, the occurrence of a defect in the mandrel test is suppressed.In addition, it was found that, in a case where the ion conductivity ismeasured after bending, a sufficiently high ion conductivity isexhibited (No. 11 to 26).

That is, by applying the solid electrolyte-containing sheet according tothe embodiment of the present invention to an all-solid state secondarybattery, an all-solid state secondary battery in which a decrease in ionconductivity over time is small even in a case where an external forcesuch as deformation is applied can be provided.

EXPLANATION OF REFERENCES

-   -   1: negative electrode current collector    -   2: negative electrode active material layer    -   3: solid electrolyte layer    -   4: positive electrode active material layer    -   5: positive electrode current collector    -   6: operation portion    -   10: all-solid state secondary battery    -   11: 2032-type coin case    -   12: electrode sheet for an all-solid state secondary battery    -   13: all-solid state secondary battery

What is claimed is:
 1. A solid electrolyte composition comprising: aninorganic solid electrolyte (A) having ion conductivity of a metalbelonging to Group 1 or Group 2 in the periodic table; a binder (B); anda dispersion medium (C), wherein the binder (B) includes a first binder(B1) that precipitates by a centrifugal separation process and a secondbinder (B2) that does not precipitate by the centrifugal separationprocess, the centrifugal separation process being performed in thedispersion medium (C) at a temperature of 25° C. at a centrifugal forceof 610000 G for 1 hour, and a content X of the first binder (B1) and acontent Y of the second binder (B2) satisfy the following expression bymass,0.10≤Y/(X+Y)≤0.80.
 2. The solid electrolyte composition according toclaim 1, wherein a glass transition temperature of a polymer forming thesecond binder (B2) is −50° C. to 10° C.
 3. The solid electrolytecomposition according to claim 1, wherein the binder (B) is one polymerselected from the group consisting of a fluorine-containing resin, ahydrocarbon-based thermoplastic resin, a (meth)acrylic resin, apolyurethane resin, a polycarbonate resin, and a cellulose derivativeresin.
 4. The solid electrolyte composition according to claim 1,wherein the dispersion medium (C) includes a hydrocarbon solvent.
 5. Thesolid electrolyte composition according to claim 1, wherein a particlesize of the first binder (B1) is 10 to 10000 nm.
 6. The solidelectrolyte composition according to claim 1, wherein in a case wherethe solid electrolyte composition does not include an active material(D), the content Y of the second binder (B2) and a content Z of theinorganic solid electrolyte (A) satisfy the following expression bymass, and in a case where the solid electrolyte composition furtherincludes the active material (D), the content Y of the second binder(B2) and a sum Z of the content of the inorganic solid electrolyte (A)and a content of the active material (D) satisfy the followingexpression by mass,0.001≤Y/(Y+Z)≤0.1.
 7. The solid electrolyte composition according toclaim 1, further comprising an active material (D).
 8. The solidelectrolyte composition according to claim 1, further comprising aconductive auxiliary agent (E).
 9. The solid electrolyte compositionaccording to claim 1, wherein the inorganic solid electrolyte (A) is asulfide-based inorganic solid electrolyte.
 10. A solidelectrolyte-containing sheet that is foamed of the solid electrolytecomposition according to claim
 1. 11. A method of manufacturing a solidelectrolyte-containing sheet comprising applying the solid electrolytecomposition according to claim 1 to a substrate to form a coating film.12. The method of manufacturing a solid electrolyte-containing sheetaccording to claim 11 further comprising drying the coating film.
 13. Amethod of manufacturing an all-solid state secondary battery comprising:applying the solid electrolyte composition according to claim 1 to asubstrate to form a coating film; and drying the coating film.
 14. Asolid electrolyte-containing sheet comprising: an inorganic solidelectrolyte (A) having ion conductivity of a metal belonging to Group 1or Group 2 in the periodic table; a binder (B); and a solvent (C1),wherein the binder (B) includes a first binder (B1) that precipitates bya centrifugal separation process and a second binder (B2) that does notprecipitate by the centrifugal separation process, the centrifugalseparation process being performed in the solvent (C1) at a temperatureof 25° C. at a centrifugal force of 610000 G for 1 hour, and a content Xof the first binder (B1) and a content Y of the second binder (B2)satisfy the following expression by mass,0.10≤Y/(X+Y)≤0.80.
 15. The solid electrolyte-containing sheet accordingto claim 14, wherein the binder (B) is one polymer selected from thegroup consisting of a fluorine-containing resin, a hydrocarbon-basedthermoplastic resin, a (meth)acrylic resin, a polyurethane resin, apolycarbonate resin, and a cellulose derivative resin.
 16. An electrodesheet for an all-solid state secondary battery comprising the solidelectrolyte-containing sheet according to claim
 14. 17. An all-solidstate secondary battery comprising: a positive electrode active materiallayer; a negative electrode active material layer; and a solidelectrolyte layer that is interposed between the positive electrodeactive material layer and the negative electrode active material layer,wherein at least one of the positive electrode active material layer,the negative electrode active material layer, or the solid electrolytelayer is the solid electrolyte-containing sheet according to claim 14.